When I started reloading, I used an RCBS Little Dandy powder measure. I'd set the cases in a loading block and bring the powder measure to the cases. When finished, I'd check the level in each case to make sure all were similar.
Later, when I bought an infinitely adjustable powder measure (RCBS Uniflow at first, a Redding 10-X later), I'd take the loading block with cases to the powder measure. Again, I'd check the level in each case after charging. I use the now discontinued Midway wooden case loading blocks which are smaller than the universal loading blocks. My powder measure stand would reach to the middle row of the case block so that I would have to turn the block around to get to the last two rows of cases. This required some discipline to avoid double charging a case but religiously doing a post charging inspection of each case would find any double charged case.
Rifle cartridges get charged by the case block method or one at a time depending on a number of factors.
The above procedures were used in conjunction with loading on a single stage press. Since I have moved on to doing lots of my reloading on a progressive press, most of my case powder charging is done on the press.
I do some rifle loading with a Harrell Precision Culver 90 powder measure. With the Harrell powder measure, I charge one rifle case at a time, returning it to a case block when complete.
The frequency at which I check the charge weights depends on a number of factors and the comfort level I have that the powder measure is doing what I expect. Most handgun loads get check once per loading block, rifle might get checked more frequently.