Some things to keep in mind:

-Once you apply a behavior to an element, there is no way to remove it

-There is no way to access the behavior by type, so if you add two different behaviors to an element, you can't (or at least, from what I can glean from the documentation) access one of the specific behaviors. This could get problematic if you have two different behaviors with identically named properties.

Just like events, being able to apply and remove things like this is very helpful.