Drop-down menus are probably the most flexible objects you can add to your forms.
Depending on your settings, drop-down menus can serve the same purpose as radio buttons (one selection only) or check boxes (multiple selections allowed).
The advantage of a drop-down menu, compared to radio buttons or check boxes, is that it takes up less space.
But that is also a disadvantage, because people can't see all options in the menu right away.
There is a workaround for this - with the size setting, you can customize the menu so it shows more than just one option at a time, but when you do that - you also lose the advantage of taking up less space.
So whatever you decide - there is always a bonus and a price to pay.
Sometimes you may want to replace text fields with drop-down menus. This might be because selecting from a menu is easier than typing. But it could also be because the script that handles the form can't interpret just any text entry.
For example, you will often be asked to choose your state from a drop-down menu. This might be because picking it from the menu is easier than typing the name of the state.
Along the same line, you may often asked to enter the 2 letter initials of your state from a drop-down menu as well.
This could prevent confusion for the script that handles the form input. If, say, the script was programmed to only accept capital letters, then a drop-down menu would secure that no invalid entries were made.
Another typical example would be replacing links with drop-down menus.
Below is a listing of valid settings for drop-down menus: