When using a dropdown, the default dropdown height is usually too low (default is 8 items for winforms, for example).
Increasing it will either save the user a click if the number of items is low or make it easier to search the dropdown if there are a lot of items.
In fact, I see little point in not using all the available space !
This is so obvious to me now, but for example, it seems even VisualStudio designers haven't figured it out (btw, if you manually increase Intellisense's height, it will stay this way, but that's offtopic:))
