I never square a log cabin block (i.e. cut fabric from the sides), but I do measure frequently when I start to be sure my seam allowance is consistent. If my measurements are good, then I can measure less frequently.
Is your question what to do now that your blocks are already sewn? Half an inch is really too much to ease in successfully to put 2 blocks of that size together, but if they're very close in size you can do a little easing, not too much or the top won't lie flat and will be difficult to quilt. If most of your blocks are one size or the other, and only a few are the other size, you can take apart the ones that are wrong and fix them by increasing or decreasing the seam allowance. One of the beauties of the log cabin block is that it doesn't usually matter if your blocks are all off from the expected size, as long as they're consistent. I would measure all the blocks, pick a size to aim at (one that would mean the least re-sewing), and then make all the blocks that size, either by shaving a sliver off to make them smaller or taking apart the block to make it bigger or smaller. You may find that you can accomplish this by removing and re-sewing only a few outer logs. Good luck.