Brake pads and removing the wheels
This might sometimes happen. The quick release is usually enough to make the pads wider than the tire, but this doesn't happen in every case.  The pads should usually be about 2mm from the rim when everything is set up.  If there is not enough room to remove your wheel after the quick release is used, you will have to loosen the cable. You can try doing this by loosening the barrel adjuster to see if that gives you the needed clearance, if not you may have to actually undo the cable, this is the least desirable solution as it makes things take a lot longer to get set up properly again.

In most cases, people only remove their wheel when the tire is flat, and so, there shouldn't be any problem getting the tire past the brakes, as the tire can be squeeze and made narrower. If you have the tire fully inflated, it can be quite firm and hard to squeeze between the brake pads. Depending on the situation, you might want to remove the air from the tire before removing the wheel, or if you are fixing a flat, don't fully inflate the tire before you put it on the bike.