Having had to estimate peak user traffic patterns, bandwidth usage, etc. for continent-scale services, Fermi estimation questions (https://en.wikipedia.org/wiki/Fermi_problem) are excellent questions for people working at the largest scales. Even if the guessed inputs or formula for the estimate are imperfect, being able to bang out an approximate formula that can brought out for discussion with peers and refined into something that can be agreed upon as a target is extremely valuable. It's not a useful skill for everyone but for those aspiring to be more than a mere coder, it's worth knowing.