Think of it like this… Moves contain:
a) a certain number of start up frames
b) a couple of active frames
c) opponents go into hit/blockstun once hit by active frame
d) move recovers
e) frame advantage is block stun minus active frames/recovery
If you hit a move meaty it means you’re hitting on a later active frame… which means less recovery… which means more frame advantage… which means more combo opportunities. The thing with SFIV is that you’ve already got tons of combo options off of links that don’t hit meaty, so the best meaty combos you can come up with are usually: meaty crouch jab, sweep. Hitting meaty also makes existing combos easier to do… a one frame link could become a 3 or 4 frame link. Now since reversals are very easy to land in SFIV… you’re going to have to learn to bait reversals lots if you want to apply meaty pressure.
Vs. some slower reversals you can actually apply meaty pressure and have your move recover before the reversal becomes active. Vs. Deejay… whose reversal whiffs on crouchers, you can go for lots of meaty frame traps as well. In order to be successful though you’re going to have to apply a standard throw mixup game to find these counter hits.
Safe jumps are basically meaty jump-ins btw. Safe jumps are probably better than meaties because jumps have less recovery and are thus completely safe from 4+ frame reversals. You can also cross-up/ empty jump low short mix-up. With a meaty frame trap you’re just applying the same standard blockstring mix-ups with more advantage.
It’s also possible to hit meaties in combos though they are entirely spacing/hitbox dependent. The idea is you hit the opponent with one move, but their hitbox is pushed back temporarily during the first active frame of the next move. As a result they get hit meaty in the middle of a combo. I know Ken and Chun-Li can combo into their sweeps this way, for example, though I haven’t seen it in a real match other than once.