Maybe there is a Pareto principle (80/20 rule) effect with these side projects: for these, you get 80% of the benefit (vs. working on it full-time) with only 20% of the hours. And for the main gig, maybe it’s 90% of the benefit for 80% of the hours. So, 1.7 for the price of 1? Sounds like free utils to me.

Plus: positive effects on employee morale/retention, skill and network building, (pseudo?) R+D / asset development, etc.

Disclosure: I’m far too dumb to work at Google. Discount accordingly.