This is true. I never do DF+RH against Mattsun (crazy Japanese N.Ken player) because he reveral DP’s it every time. Don’t ask me how.
Also, there are certain characters like Honda where you don’t want to do it, because you have much better options. (Just throw a meaty fireball against Honda. If he buttslams through it, punish him. If he doesn’t, keep him zoned with more fireballs.)
Also, you should never do it against Blanka, because he can reversal ball (either ball will work), and because he’s airborn, he will not be knocked over, but YOU will be. That’s bad.
-When you’re opponent doesn’t know which way to block it.
-Against Dhalsim and Dictator, because they have no way to reverse it (unless Dic has super).
-Against the characters that it can cross up: Ryu, Ken, Guile, Hawk, Cammy, Fei, DeeJay, Boxer.
Against Boxer, I prefer safe jump j.Forward, then make him guess between cr.RH or throw. That, or meaty cr.Forward, cr.Fierce.
Against some characters, I like to simply let them get up and see what they do. Especially characters with good reversals, like Ryu, Ken, Cammy, etc. People want to do that reverasal, so let them whiff it, then punish.
I would almost never do it against Honda, and definitely never against Blanka. Whether or not you should do it against Gief/Hawk is also questionable. You do get free block damage with the lightning legs follow-up, but it’s REALLY bad if you mess up, because you just closed the gap, which is doing his job for him. You want to stay away.