We've done that with very good results. There are benefits to be had from protecting the application from the "messy" database design: if you normalize your database design - as you should - the database tables often bear very little resemblance to wwhat the user sees. Keeping that mapping in a tightly controlled module is Good(TM). Further benefits are to be got from using stored procedures (as Abigail-II notes)

Having the front-end (user and possibly badguy accessible) macine not having direct access to your valuable database is also a security bonus.