Use a belt or keep going?

First of all I'd like to thank you for your novice program. It's given me great gains.

Second, I'm up to 335x5 on deadlifts but I haven't put on a belt yet. My work sets don't feel particularly difficult, especially when I warm up properly and apply the valsalva maneuver, but I do usually feel soreness in my lower back for about a few hours after the session.

Many people, especially my friends and people at bb.com, say to put on a belt, but isn't it better for my strength to deadlift without one?

Thanks.

No, a belt is a damned useful tool if you are judicious about its use. You can make a harder ab contraction against a belt than you can without one, and it allows you to safely lift more weight than you can without it. I'd use it if I were you.

should one use a belt when squatting?

if one needs to

what indicates the need to use a belt in the squat?

the weight gets real heavy