Here's a good example of why you should do it.  I had my left ACL done in March of '04. I tore it again in September of '04.  I got an ACL brace, the one you see on all of the O-lineman these days, and kept running around with that on.  I tore cartilage 4 times since then, even though I had built up my leg muscles, due to not having the ACL.  I finally gave in and had it redone a month ago.  I am now giving up all of the fun things that involve running around because of all of the cartilage damage from me not getting the ACL redone years ago.....just saying.