Currently, if we want to add a content part to a content type, we'll see a list of available parts. At the top of the screen there is a help text stating: "Choose the Parts to add to this Content Type. Adding the Containable part makes it possible to add
content items of this type to a List."
That is useful information related to the Containable part. Similarly, it may be helpful to users to have a short description of other parts as well.
If each part could have a short description, it could be rendered next to the name of each part (I'm thinking of a table here with 2 columns).
Or instead of showing the descriptions all at once, we could add a small help icon which the user can click to show a tooltip / balloon.
This help text could be implemented as a setting on the content part.