One ATC was handling helicopters and planes. It’s supposed to be a Controller for each, but they do allow doubling up during low traffic... but if there was an incident yesterday, I would think one wouldn’t allow doubling up on the responsibility today!
At many events where they have a sign language interpreter signing what the speakers are saying they have two interpreters switching off because it is so intense to sign and each one needs a frequent breather.
I would think being ATC and interpreting all of the blips on a screen is intense and breaks are needed.
It seems like it would be a good idea to be regularly a little it overstaffed at the tower. Directing air traffic is, after all, a matter of life or death.
What if an ATC gets a migraine attack? Or gets a call that there is a family emergency?