I try to ride in a snaffle where possible, however obviously this is not always best! I used to use a stronger bit out hacking because my horse had a tendency to bolt when he was younger, and not having control got quite dangerous. I switch to a stronger bit now only in situations where I need control, such as when I need adjustability in his stride for showjumping, or when he leans on the bit and pulls going cross country. I used to struggle in a snaffle even for dressage, but I have switched snaffles to one that has a sweet iron and copper mouthpiece and encourages him to accept the bit. This has really helped me as my horse loves it, so I can hack and jump in a snaffle with pretty good control now!
I only bump up to a stronger bit to touch up areas in my training, for example, my gelding was getting really low and heavy in my hands in the pelham, and I bumped him up to an elevator for a little bit to strengthen his topline so he could carry himself better. When I change bits, its to make the touch-up training easier on myself. Its so you can teach your horse without struggling yourself :)
If you struggle to slow your horse down or he is able to do what he looks sometimes it’s probably time for a stronger bit!!