I know what the relocation bracket does re-centering the axle and whatnot but how critical is it to install with 2.5" of lift? I just put my lift on over the weekend and I didn't do anything with either track bar. Is this something I should get and put on or am I fine without it? What are the pros and cons of relocating the rear track bar? If I don't do it is it going to hurt anything short or long term?
A 2.5" - 3" lift will pull the axle over about an inch if I remember correctly. You can measure and see for yourself. Pick the same (clear) space on the frame on either side and measure to a noticeable point on each tire and you will find your distance. Brackets are cheap and will get you lined up pretty good so I would just do it.
If you use the bracket or adjustable trac bar you are lined up better to reduce drive line issues, and keeps tire clearance between the frame even which helps a lot if you don't have wheels with a low offset #
It will look pretty stupid if your axles aren't centered under your jeep especially when only one side of it is covered in mud and the other is clean. Do the job properly and centre everything up don't do it half assed.