For me at least, I can use it as a weapon and throw it in occasionally to throw the opponent off guard. I wonder why the pros don't use it that often(other than when on complete defense).
People don't use the forehand slice anymore because there are more effective options off the forehand wing.
For instance, if player A slices to player B's backhand, player B will likely slice it back. (Percentage tennis is to slice a slice) especially if player B has a 1 handed backhand. If player A sliced to player B's forehand, player B can attack the slice with a topspin forehand, a reverse forehand etc more offensive shots than a forehand slice.
Fabrice Santoro on the men's side hits basically a 2 handed forehand slice as his forehand and it is clearly his weaker wing.
Hitting a forehand slice is a good way to get on the defensive in a point real quick.
Another thing is slices are lower percentage than flat or topspin shots. The underspin causes the ball to travel further so it has to be hit closer to the net if you are going to hit an offensive
slice. Whereas topspin causes the ball to dip down into the court so you can hit it offensively with more net celarance and it will still drop in.
This is critical if you are hitting with power and pace.
What level do you play? You need to play better people if people aren't eating up your slices.
Once I see my opponent is slicing I get to that ball FAST
. Get into position, BEND MY KNEES and hit a topspin drive. Usually my opponents slices have sidespin on them as well so the ball ends up moving away from me so the more reason I have to get there quickly. Also to get the ball before it gets too low. Slices give me NO trouble now.
The only time I hit a forehand slice is when I'm pulled out wide and I hit a squash-shot type slice to get back into the point or I'll hit a forehand slice-lob to buy me time to get back into position.