Is it possible to limit how many times and entry type can be used?
If you're working with frontend forms, set the permission to use any of these entry types to a specific user group or to admins only. Use isInGroup or the admin property:

{% if currentUser.admin %} ... {% endif %}
{% if currentUser.isInGroup('usersWithSomeEntryTypesHidden') %} ... {% endif %}


If you need this in the CP, you could make a plugin that does the same and hides selected entry types from the dropdown using JS. As this is no nice solution, what about making this a feature request to Pixel &amp; Tonic?