Loading cases of differeing length can be done, but it is more tedious. If you don't have a trimmer, you should sort the cases into batches by length, using a caliper. If you don't have a caliper, get one before you get into serious reloading. They are not all that expensive, and are indispensible for a great many things. A case length gauge is handy and useful, but it does not replace a caliper.
I agree that a case length guage cannot fully replace a caliper, but I do feel I should add that the Lee case trimming system will accurately and rapidly uniform the lengths of fired cases to the SAAMI default for the particular caliber you buy the tool for. Midway has them for dirt cheap $. I have yet to get any for my pistol calibers, but I am very impressed with the tool's quality for my .308 and .30-30 handloads. I usually get 1-2 small tools with each midway ammo order, and these are on my "want" list for each pistol caliber.
But, my case length trimmers sit right next to my calipers.