[kaulquappe]

Economically, it's usually more expensive to use serverless functions for a constant level of load. At least on AWS but I'd be surprised if the math turns out differently on Azure. So your intuition (low traffic or bursts) for serverless is quite correct, IMO. I usually try to move any stuff that doesn't fit with typical web server loads to serverless functions, e.g. cpu-intensive one-time tasks like image resizing or generating argon2id hashes, etc. But even for those loads it might be more economical to put them on separate instances/scaling groups if they can saturate those and the load is predictable enough.