OK, and compared to what? "Less" is a comparison, but you didn't specify what you're comparing Debian to.
Out-of-the-box RAM usage is a pretty specious metric because you're not installing Debian (or any other OS) just to have sit there in its out-of-the-box condition. Do you think a Debian server running Apache with 1000 vhosts will use less RAM than a RHEL server running nginx with 10 vhosts?
Debian uses like 200MBs of ram for a basic fresh install. That’s negligible.
Unless you’re deploying 500 virtual machines on a single server, that all run a single simple basic task the base ram usage of the OS shouldn’t even be a factor.
I think this is a fairly common use case. Maybe not the most common, but I’ve definitely seen this at multiple shops.
Density of RAM on hosts is often a limiting factor for scaling. Not every app is CPU hungry. Some just need to be available, and running a whole is for isolation is the way it’s done in a lot of shops.