reducing the risk of allowing users to inpur crap data
stupidly allowing developers to confuse presentation with storage by presuming a format dictates how data is stored (a classic case being people who assert that because their date format is dd/mm/yy or mm/dd/yy or whatever thats i how its stored. Although even mnoire stupidity can come in from encouraging develoopers to store data in the wriong format (eg numbers as text, or dates as string). or dtaes and times n different columns, or breaekign a datetime valeu into different columns (eg a column each for hour, minute, second...)
input masks can give a user a hint as to how the data should be presented.
it can constrian data to certain formats (eg you can sepcifiy if it shoudl be all upper case)
Im sure there is plenty more that can be said ont he topic f you google it...
I'd rather be riding on the Tiger 800 or the Norton