In some traditions commentaries are inherent in the daily sermons and books written by monks. But I've noticed that most of the commentaries are not available digitally in English compared to the Suttas and most people don't use commentaries as reference.
Are they not so important or what is the view on commentaries?
In Theravada Buddhism, much of the commentarial literature is merely providing definitions and etymologies of words, so it only makes sense in the original pali. Besides this, it is so voluminous that any attempt at translating it would be a daunting task.
That being said, some of the more accessible and interesting commentaries have indeed been translated into English:
I'm sure there are others, but this is a sample.
As to their significance, in Theravada Buddhism, they are what defines the orthodoxy; any interpretation of the canonical texts that deviates significantly from the commentaries is considered to be outside of the fold of Theravada Buddhism. In a word, they are the agreed upon correct interpretation or explanation of the texts.
And they have some funny stories.
Commentaries are just further explanation of meaning and details of the Suttas. Each explanation is subdivided into more details.
E.g. If I ask you to come here. This can be the instruction in the Sutta. The commentaries will go on saying if you are facing another direction to 1st turn towards me, then start taking steps towards me, then when you are at a reasonable distance stop. The reason I might have called you and in which situation I would have called out.
If you can understand and follow the Suttas you need not rely in the commentaries. May find it difficult though. Sometimes certain aspects are explained elsewhere in other Suttas. So doing so might require a scholarly understanding of all related material.
You should take commentaries with a pinch of salt as there can be errors, omissions and miss interpretations like with any other publication / book. Otherwise they can be useful to get and idea of the social customs, background or event leading to the preaching. Also they consolidate from other areas in the Tripitaka too in some cases which can be useful.
When practicing something the final litmus test is to compare with the insight you get at the experiential level. This would help find any inconsistencies. Also some of the later commentaries have correction mentioned about the previous ones. This can be also put to the same test. The errors are very minor though they can be a stumbling block, if you hold on to the belief too strongly. Hence they should be used for additional guidance and information but again being diligent about what you pickup from the source.
Commentaries are very useful when interpreting the Suttas in the Tipitaka. They provide background stories and additional details. It is wrong to assume that when they wrote down the Tipitaka, they included everything the Buddha had preached. The major commentaries were based on earlier ones, which were written down at the same time as the Tipitaka. But even the ones written later shouldn't be treated lightly purely on that basis. It's a bad practice to degrade the commentaries on a whim without solid evidence. But if you have a different opinion on a topic, it is ok to say "this is what the commentary says, but this is what I think". Then it becomes your own commentary. :)
