Typically, “dropping a foot” in a corner is not done to actually touch the ground with your foot but to change you balance on the bike. Putting a foot out to catch yourself “just in case” is usually a really bad idea.

It is useful sometime, but whether and when it is worth doing really comes down to how fast you are at getting back in the pedal, and what it is like riding before you do.

I use Frogs and can be clipped back in by the end of the next pedal stoke, so I drop a foot in a corner whenever it feels good.