This is only true if you do two unrelated things simultaneously: have a monolithic repo, and keep the whole thing checked out at all times. Provided you have a sane build system (pants, Blaze, Buck, etc.), then the only thing that should need to have the full checkout is the CI server; you should be able to safely work from a narrow clone.

That said, I find your note a bit amusing. I'd have agreed a decade ago, but nowadays, 50 MB should take effectively zero time for you to both download and apply. It's worth revisiting things like this as LANs and the internet get faster; I think the speed comment is a bit outdated now.