can someone explains the benefits of a weight belt?
What do you mean by "weight belt?"
A belt to support your back, or a belt to add weight to your frame? Although I suppose if you can answer that you can probably answer your own question. Why not post a picture of what you're referring to.
the lower back belt
A belt that size and thickness is used primarily to prevent injuries. By wearing one while squatting and deadlifting you'll decrease the chances of injuring your back due to poor form and control. On some of the thicker and wider belts you'll notice an increased in total poundage lifted compared to lifting without one. Most people attribute this to stabilizing the lifters midsection.
It helps support your lower back while squatting.
The downside of wearing a belt is that it takes the core muscles out of your lifts. This actually worsens than problems rather than improve it. Why not strengthen your core and lower back muscles so they can do their job properly: stabilize your body during every single lift. As a beginner, you shouldn't be going so having that a belt is necessary.
Generally speaking belts should be left to powerlifters (because they move serious tonnage) and bodybuilders (I've read they use belts to "shrink" the waistline or something along those lines).
There are none.
Going belt-free: Good enough for Konstantinovs, good enough for you.
Increasing the internal pressure when preforming the valsalva maneuver.
If you're wearing a belt make sure that you still actively "press out" against the belt so that it supplements your own support structure instead of trying to replace it.
Also at the end of his very last rep he says "Like this Ha ha ha". All other words are gibberish to me.