Actions after which I expect some kind of response seem to be more costly than the direct time cost they incur (for me, at least).
They also incur a decreased effectiveness of the time just afterward, due to causing me to be anticipatory – e.g. I am more likely to check up on whether I have received a response, and empirically find it generally harder to focus.
Examples of such actions
Ways to combat this cost
I am curious who else has or hasn't noticed this kind of cost, and whether anyone has ideas for combatting it (my guess is that the policies I am currently operating under don't respect this cost enough -- e.g. I made 3-5x more progress toward my most important goal while on a plane yesterday than while not on a plane today, and it seems like if I had better mechanisms for appreciating the costs of being anticipatory, this difference could have been at least 10% smaller).
Cal Newport frames this problem as the "hyperactive hive mind" in his book "A World Without Email". He suggests that the solution is more structured communication, rather than ad hoc communication. Its lessons on email helped me a lot at work, so if this is a topic that bothers you too, I would suggest checking that book out.