In general it makes sense to use existing ICU beds at capacity (or slightly below), to, you know, make use of them.
Surely you could also still adjust by delaying surgical procedures that are not urgent, if things would get worse.
As for nurses working overtime, do you have any data for that? Quoting some individual hospital managers warning of "possible collapse" is not really evidence. They can also be politically motivated ("see, we really need more money for our ICU section"). You can also find individual hospital managers saying everything is fine.
https://www.intensivregister.de/#/aktuelle-lage/kartenansich...
If you can read German here is a source for Berlin: https://www.tagesspiegel.de/berlin/zu-viele-corona-patienten...
TLDR is only 85% of the beds are full, but there aren't enough nurses, so the emergency room will be closed. Several other hospitals in Berlin already stopped admitting new ICU patients.
https://www.welt.de/regionales/bayern/article161869919/Klini...
https://www.researchgate.net/publication/333785335_Managemen...
And if it is really such a limiting factor, the statistics should be adjusted accordingly.
I think it is just a wildcard argument without any specific numbers. You can imagine whatever you like. How many nurses are available? How many are sick, specifically?
Also, sick nurses tend to be well again after two weeks (if they have Covid).
Optimal rate depends on the country, but about 75% is typical.