My car (bit of an extreme example) could be pushed side to side on the subframe. (Bushes really old)
When throwing the car around corners, with the big rear bar, there was still a noticable amount of movement, to the point of the rear end feeling like I had 4w steering or a popped Tyre in the rear. The locking bolts fixed that
+1 for alignment, had to move my whole subframe about 20mm to get it to all line up, didn't have a chance to get it done before a long trip, destroyed a set of rear tyres in 1500km