Most people are under the misapprehension that a pre-approved mortgage means they are guaranteed financing. Nope. That’s wrong. Just because you're pre-approved doesn't mean you're guaranteed financing. The lender can still say “no” if the home you've chosen doesn't meet their lending criteria.
What would you do if your banker then turned around and said, “Sorry, you're not approved”? According to your offer, you must close. Failure to do so would result in foregoing your deposit (and how long did you scrimp and save for that?) and opening yourself to legal action. So you must still make your offer conditional on financing.
Conditions on an Offer to Purchase aren’t popular with real estate agents since conditions are one way a sale can go south. So many agents encourage their clients to bring in a “clean” offer – one without any conditions. But if you do, you only have yourself to blame when you discover you can’t close because your financing fell through on a technicality. Oooops.