You must be confused if you think that I only have one or two of any mags! Nor did I say that you should only purchase 40 round mags, so you are not loosing any "versatilty". Buy the size that fits your intended purpose.

I just like the idea of not having rounds left over to make a partial box, so I like the idea of simplifying:

1 box = 1 20 round magazine
2 boxes = 1 40 round magazine

However, if you have enough magazines on hand, you could buy a 500 round case and you can fill 12, 40 round magazines, or 16, 30 round magazines, and have one 20 round box left over... so, for every 480 rounds do you want to change magazines 12 times or 16 times?