The aspect of “transaction cost” for doing a particular thing once or multiple times is interesting.
Starting a bunch of things in parallel will often lead to many being finished at a similar point in time, often all at once and leading to the dreaded ‘big bang integration’, which even in short sprints may be painful enough already.
That said, I love starting multiple things at once. Sometimes being ‘stuck’ on the same thing and not having some other outlet or diversion to put your mind to makes a task take longer. Having the ‘diversion’ often gives me more energy to breeze through the other task… and sometimes it doesn’t. It’s not scientific.