In all honesty, I've loaded both ways. Much depends on the cost of the brass. Some is so cheap its not worth the effort to resize, knowing full well you may end up tossing a few cases.
Others are so expensive its only prudent to take every precaution. An example of it is oddball magnum brass, like .30-378. With each empty costing between $2 and $4. With those you not only size each case, but you trim to length. Just to be certain.
Its easier with once fired. You can just adopt the method of of resizing and checking the length with a caliper if you have any questions.
With the new, unfired cases if you have any questions, the easy way is to sit down, open the cylinder, and test fit every last case. Start with 2 identical containers. Like Tupperware, or the generic equivalent. Fill one with the raw cases. Then fill the cylinder and dump each into the empty one. As you move along, you'll get fairly quick about it. Be careful because the indication you're looking for is one that just hangs up before seating. But usually they seat by themselves, no questions.
And that can also be your final QC check. Fill the cylinder then dump it. Its even easier with loaded ammo because its weight helps. If there is one thing I can't stand is a round, any round, that doesn't chamber or seat. If its my reload, I blame my self for poor quality control. It doesn't happen these days because I learned my lesson long ago.
This relates to the OPs question because if he doesn't want to resize, he can skip it if he checks each round as part of the process.