Quite. I suppose it might make sense, if you were doing development on a really space-constrained embedded box or something -- but I hope you're never running a compile on that sort of machine, or you'll be waiting for hours and hours.
(Alternates aren't ideal -- one fetch in the wrong place and oops you suddenly have heaps of redundant objects since you need to pull in the other place too and you probably don't have them set as alternates of each other. You need to be quite rigid in your fetching habits if this is really to save you a lot of space. But, heck, I do that sometimes and it just vanishes in the oceans of space on my multiple-year-old obsolete small disks. Even the *Chromium* source tree vanishes in the oceans of space on those disks. Disks you can actually buy nowadays will be even larger. This argument will never fly.)