There are different directions one can go in here. For instance, there are a number of cartridges that will function quite well with the same powder.
For me, and referring to bottle neck loading I like to load with powders that will produce optimum performance for a particular cartridge and bullet weight, but one powder can often serve multiple cartridges / bullet weights with optimum performance also.
An example of picking optimum powders for me would go something like this. .243 win. 100 gr. bullet. I would go with RL17. But if the bullet was lighter, say an 65 gr., I would probably go with RL15.
Then something like .270 win would have it's optimum for my desired needs. Say a 130 gr. projectile, RL17 would work very well, and would also serve as an optimal powder for the 243 win 100 grain as well.
And even when stepping up to something like the 7mm RM, there are options that will function fairly well for the .243 win, 6mm Rem, .270 win, 30-06, and numerous other's, as well as the 7mm RM. I would sacrifice something, some where by using a single powder for all of them. But it can be accomplished, and with fair to good results, just maybe not optimal by my standards. About the best way to pick is to study the data and find powders that meet your desired performance level, then try a few and see which of those best meet your expectations. Some approach it from an economic stand point, others may desire velocity, and yet others may be seeking the most accurate load.
That is how I like to do it though. But by no means is it necessary to work it like this, there are certainly many powders in which one powder would produce good accurate performance over a broad range of cartridges and projectile weights. But this is one of the aspects of reloading, for me anyway, that has drawn me into the hobby in the first place, the fact that I can, that is what makes it so fun for me.
GS