Its all based on what axle you have. Dana 44, properly geared is fine with 35's. 37's start pushing strength limits. You can still run 37's but your going to want to upgrade your steering, brace your gear box and regear.
I would run no higher then a 4.88 with 37's and would more likely end up with a 5.13 or a 5.38 gear. 4.88 gears are still strong in a dana 44 and 5.13's are pushing it strength wise. You should also think about running chrome moly axles if you drive hard. Again, its all based on what the vehicle came with.
If your just putting around on forest roads with mild to slightly moderate trails, your going to be fine with un moded vehicles with 35's but you loose a ton of torque if you don't regear.
If you run a TJ or older vehicle, your doing mod's sooner then an 07 or newer.
My viewpoint is going to be a bit biased because I drive on harder trails then most.