With certain projects, such as projects that involve separate frontend and backend codebases, I use a separate tmux session for each. This means that for certain tasks and features I find myself flipping back and forth between them constantly.
This can get tedious with an approach like <prefix> s where you then have to
find and select the other session from the list.
A more efficient alternative is <prefix> L -- this takes you to the last
session. So, if you are in the backend session and had previously been in the
frontend session, then hitting <prefix> L will immediately place you in
frontend. Hitting that exact same binding a second time will take you right
back to backend.
See man tmux for more details.