A few times a week I go cycling with friends, we usually go to off-road places with jumps. I was wondering if having the saddle further backwards or forwards would affect performance?
The fore and aft position of the saddle is a highly personal position. You're going to have to experiment with it to find where the saddle should be for your style of riding, terrain, your proportions and your bike. Peter White has an article on bike fitting, which may be of interest to you. The most relevant passage is:
take the case of two riders; Rider A, and Rider B. Rider A has very little upper body muscle but very strong legs. Rider B is identical to Rider A but has been working out at Ralph's Gym and looks like a body builder. The fore aft position of the saddle will be slightly different for the two riders. The extra upper body mass of Rider B will require a slightly further back saddle position to give the same balance. But that doesn't necessarily mean that Rider B should have his saddle further back. He may prefer the more forward position. Only he knows what his preference is.
Note that for mountain biking, you also have the option of moving the saddle up and down if you install a dropper post, which can also be useful depending on your riding style, terrain, your proportions and your bike.
Depends how you personally make your power. When climbing a long steady grade, either road or offroad, you recruit different muscles depending on your angles.
Sliding forward on your saddle uses more muscles under the thighs, and sliding backward uses others.
So, if you move your saddle forward you're increasing time on some muscles and denying yourself time with the others.
Ideally you want your body in a middling position to allow you to be forewards or aft as the need allows.
Personally I like to be forward on a climb but will sit back to recover for some sections, and I like to be average on a descent and turns, but ready to push weight backwards for braking.
You need to try variations for yourself, and dial in what fits.