is it beneficial to have both a one-handed and two-handed backhand?

Yes it give u more shots to use in the game.

I have both and think that it is extremely beneficial to my game. The 2-hander is my rally shot if I'm playing a player with power. If not it's my put away shot. I use my one hander for drop shots, lobs, slice and occasionally a normal shot just to throw my opponents timing off.

Yes, it is beneficial. One thing, when your opponent sees you using both, you might surprise him and take his mind off the game. And the main reason is because you can't always get into position to hit a full two-hander, and it's easier to get into position for a one-hander while on the run.

IMO, one-handers are better for control, aim, taking chances, and sporadic power and two-handers are best for consistent shots and consistent power.

you should learn the one handed backhand slice like all pros who use the two hander. its useful if you have to stretch to reach a ball. the spin on the ball causes the ball to float slowly back to the opponent and bounces low, giving you more time to recover.

another benefit is that learning the one-handed slice improves your volleying skills on the backhand.

Yes. All the pros basically have 2 backhands, even Federer. It doesn't matter whether your top-spin backhand is 2 hands or 1, having the 2 different backhands is very beneficial for defensive reach considerations, slices, etc.

I believe so. Especially when you need reach the one hander will be a good advantage.

i like the one hander better because i get more control of the ball.

it is handy when you need to reach for the ball