It depends on your sort order. If your goal is to only display the most recent 'featured' entry, then you could add the .first parameter to your template code.
Craft would simply grab the first entry it finds
OR, you could limit your query by using the Limit parameter. See: https://craftcms.com/docs/templating/craft.entries#limit
Edit (addition):
Here's an example of how you could display the single, most recent entry which has been marked as Featured, using a lightswitch field.
{% set featuredNews = craft.entries.section('news').featured('not 0').order('dateUpdated desc').limit(1) %}
{% for entry in featuredNews %}
{{ entry.title }}
{% endfor %}
(Some valuable insight here: craft.entries and lightswitch and here: https://craftcms.com/docs/lightswitch-fields)
Hope it helps
Limitparameter, used to filter entries with the switch turned on, then used in conjunction with the.firstparameter might work. It would only take the most recent article that has the switch enabled; it's nowhere near a perfect solution though. – jasonetco Mar 29 '16 at 00:15