I think a lot about communication, especially as I'm currently working in a team of size one.
The main thing I think about communication is how expensive it is, especially synchronous communication.
And this isn't "meetings are expensive". Literally all communication is expensive. It takes up a lot of time, and unless you're very careful about your team topology that time grows quadratically in the number of people in the team.
The benefit of adding people to a team is rarely that it improves your efficiency: All things being equal, a small team will outperform a big team at a task they are both capable of achieving.
The big difference is that a big team is capable of achieving many things that a small team is not. Either through sheer amount of work they are capable of doing, or through the fact that they represent more skills than small team can have.