The problem is finding people who know how to fit mountain bikes and are qualified to do so. Being a good rider isn't a qualification. Being a good mechanic isn't one either. Neither is working in a bike shop. These people might help you fix things that are egregiously wrong, but they aren't going to be able to fine tune things like bar width, bar roll, lever position, etc really well.
I've had fits done to address specific issues early on when I started riding and it helped, but the person I got fit by had extensive experience as bike fitter for decades, knew mountain bikes, knew current trends in mountain bikes, and how to adjust based on riding styles. That's not super common and most fitters you find are going to be really road, gravel, or XC focused, at best. For that reason alone, I'd not bother with unless you are certain you can find someone that knows mountain bikes and can demonstrate experience fitting bikes to people the way you ride.
A lot of people will tell you it's not needed for various reasons. That doesn't reflect my experience at all, but there is some truth there in the sense that most bike fitters have no clue how to fit to most modern mountain bikes. RAD included.