For the Find Steed spell, what does it mean to bond with your steed and "fight as a seamless unit"?

Question

The description of the find steed spell says (emphasis added):

Your steed serves you as a mount, both in combat and out, and you have an instinctive bond with it that allows you to fight as a seamless unit. While mounted on your steed, you can make any spell you cast that targets only you also target your steed.

What does "fight[ing] as a seamless unit" mean?

There's no fluff text, right? Perhaps it is just introductory to the following sentence about a spell affecting both rider and steed. That seems to relegate it to fluff text, though, if the sentence could be omitted without changing the meaning. I'm not sure there's a RAW answer, at least I can't find a specific one.

If there's no RAW specific meaning, and it isn't fluff text, what's a reasonable interpretation of this line?

Answer 1

I give advantage on riding related Animal Handling checks.

This portion of the spell description was pointed out to me by the paladin in one of my games. She wanted to leap over a smallish stream mid-combat, so I called for a Wisdom (Animal Handling) check, based on the Player’s Handbook description of Animal Handling:

When there is any question whether you can calm down a domesticated animal, keep a mount from getting spooked, or intuit an animal’s intentions, the DM might call for a Wisdom (Animal Handling) check. You also make a Wisdom (Animal Handling) check to control your mount when you attempt a risky maneuver.

After I asked for the check, she quickly asked for advantage, quoting the “fight as a seamless unit” portion of the spell description. I thought about it for a moment and have stuck with the ruling ever sense. To me, it makes perfect sense that being able to communicate telepathically with your faithful and intelligent mount should have some advantage over riding a stupid beast.

Answer 2

The Mount can be counted as independent and expected to do as you wish.

The PHB, page 198, says the following about mounted combat:

While you’re mounted, you have two options. You can either control the mount or allow it to act independently… An independent mount retains its place in the initiative order. Bearing a rider puts no restrictions on the actions it can take.

What this means is that your mount can attack on its turn in combat, whereas a typical controlled mount can only dash, disengage, or dodge.

Answer 3

It means exactly what the spell says

So it's apparently well-accepted that "5e has no flavour text". Fine; I'm not personally sure that's actually true, but let's assume it is. Every part of that spell text is meaningful in that none of it describes something that isn't actually happening in the game. You definitely have an "instinctive bond" with your mount and can fight with it as a "seamless unit". What does that mean?

Let's look at another example. Here's the paladin's Divine Sense ability:

The presence of strong evil registers on your senses like a noxious odor, and powerful good rings like heavenly music in your ears. As an action, you can open your awareness to detect such forces. Until the end of your next turn, you know the location of any celestial, fiend, or undead within 60 feet of you that is not behind total cover. [...]

Here's an excerpt from twitter showing us what the author of the rules has to say about how to read them, in the context of interpreting the paladin's Divine Sense ability:

Beats @Beats_Alive · Apr 30, 2018
Morning @JeremyECrawford! My group's Paladin seems to think he can Divine Sense someone's alignment and whether or not an item is cursed. From what I understand, the first sentence is meant as flavor text. Could I get clarification?

Jeremy Crawford @JeremyECrawford · Apr 30, 2018
Divine Sense doesn't detect alignment or curses. The feature's text explains what it means by strong evil and good: fiends, undead, celestials, desecration, and consecration. #DnD

dandanfielding @DMdandanfieldng · Apr 30, 2018
So the first line is flavor text, then? There are people who insist every word in the rules have mechanical impact while others state that some, like the first line of Divine Sense, are just flavor with the "crunch" following after.

Jeremy Crawford @JeremyECrawford · Apr 30, 2018
In any piece of writing, context matters. If a rule has multiple sentences, they're meant to be read together. For example, the first sentence of Divine Sense is meant to be read with the rest of the feature's sentences, which explain that first sentence. #DnD

Here Jeremy Crawford explains that often, the rules are written such that one sentence may say a thing and then the following sentences explain what that first sentence meant, providing context and clarification. Divine Sense says a thing that is vague - paladins can sense strong evil and powerful good - and then immediately explains what it actually means when it says that. The fact that the ability is actually more restricted in scope doesn't make the first sentence not true (i.e. "flavour text"); paladins can detect certain kinds of evil and good.

This is the exact same sort of text as in find steed.

Your steed serves you as a mount, both in combat and out, and you have an instinctive bond with it that allows you to fight as a seamless unit. While mounted on your steed, you can make any spell you cast that targets only you also target your steed.

You have an instinctive bond with your mount that allows you to fight as a seamless unit. What does fighting as a seamless unit mean, in this context? It means that you can affect yourself and your mount with certain spells as if you were a single person, both enjoying the benefit of a spell that normally would only affect you as an individual; one might almost say the spell observes no seam between you and your mount.

This isn't a circumstance where the rules say a vague thing and then don't explain it and we have to figure out what it means; this is a circumstance where the text immediately explains itself. You are not meant to try and infer some kind of extra benefit beyond what the spell itself explains about how it works.