The main benefit of the one-handed backhand is the extra reach that the shot has as a result using of the non-dominant hand less. Although the single-handed backhand is a very difficult stroke to learn and master, players tend to have a lot more reach and can hit through the ball easily with a lot of top spin once the stroke is mastered. It is much easier to play attacking shots with the single-handed backhand as the player tends to hit the ball more out in front of the body compared to a double hander, which is highly suitable for an attack minded player who loves to come to the net and finish off points.
Another added advantage of the single-handed backhand is that the player can disguise the backhand slice a lot better, which will constantly keep the opponent guessing and makes them unsure as to how to close out the point. The reason behind this is that a single-handed player has a similar release technique for a flat shot or a slice shot.
An additional bonus is that since backhand volleys are generally hit with one hand; single-handers tend to have better feel and technique on their volleys which is crucial when it comes to closing out points and for players who play doubles. This is probably the reason why majority of the doubles specialist players play with a single-handed backhand, rather than a double-handed backhand.
The biggest drawback of the single-handed backhand is that it is very difficult for kids at a young age to learn the skill, owing to the difficulty, strength and control required in the hand which kids usually do not possess at a young age.
Compared to the two-handed backhand, the one-handed backhand typically generates less power due to the use of only one hand. This can make it more difficult to hit winners and penetrate through an opponent's defense. Also requires greater balance and stability which can make it more difficult to execute consistently, especially under pressure.
Most kids are taught a double handed backhand by tennis coaches owing to the fact that the second hand gives a lot more stability and power to the shot. As a player gets older and stronger, they may choose to switch to a single-handed backhand depending on their style of play. However, in modern day tennis most players tend to stick with a double handed backhand even when they start playing professionally.
One significant advantage of the double-handed backhand is hitting balls that are above the waist, which are much easier for a double hander as single handers tend to struggle with balls above the waist due to the lack of control. A good player will take advantage of this weakness and tend to hit loopy balls to a single hander, but this tactic will not be useful against a player with a good double handed backhand. With a two-handed backhand, a player tends to get away with a poorly timed shot and recover more easily than a single hander would which is another huge bonus.
The two-handed backhand allows players to create more topspin on their shots, which can help the ball stay in the court and bounce higher, making it more difficult for opponents to return.
With both hands on the grip, players may have difficulty reaching high shots or balls that are above shoulder height.
Players using a two-handed backhand may struggle to return slice shots, which can stay low and skid through the court, as the grip may limit their ability to adjust quickly to the ball's movement.