I don't think it will matter much one way or the other if you keep it or not, it's only attached to the lower framerail lips. Perhaps it could offer a little protection for the driveshaft while offroad, though it still wouldn't be protecting the most vulnerable part of it (right near the rear axle flange).
I agree....I originally kept mine when it had the 4" lift, but once I went higher than that I had to remove it to prevent rubbing. I was skeptical at first, but it doesnt affect anything and you'll never know its gone. Its still possible to relocate it forward if you feel the need.
I have 5.5 inchs of lift and i never had to move my cross member or trim my gas tank but my one piece shaft is not aluminum its steal so maybe its not as big as around. hadn't really took it off road since i installed it either so i dunno if its gonna rub or not but it looks like it got plenty of clearnce.
Interesting...You must not flex your suspension much then. At 6" of lift I couldnt even drive through my yard without it rubbing the gas tank skid plate, and thats with a steel driveshaft (the larger aluminum would be worse). If the awful noise wasnt enough to confirm it, the marks on the driveshaft were. With the vehicle at ride height the driveshaft doesnt sit very far away from the crossmember either and can come in contact with it offroading. I didnt even chance it by driving....Grabbed the angle grinder and went to town.
So to recap...
At 0-4" of lift, you can get away with keeping the crossmember during light wheeing and slight trimming of the gas tank skid plate if needed.
At 4-6" of lift, the driveshaft is pretty close to the crossmember and will come in contact with it if you flex your suspension. Gas tank most definitely will need some triming, but the amount is determined by the diameter of driveshaft you have (smaller steel vs larger aluminum).
Hope this helps someone...