The main downside to not having swap is that Linux may start discarding clean file backed pages under memory pressure, when if you had swap available it could go after anonymous pages that are actually cold.

On a related note, your program code is very likely (mostly) clean file backed pages.

Of course, in the modern era of SSDs this isn't as big of a problem, but in the late days of running serious systems with OS/programs on spinning rust I regularly saw full blown collapse this way, like processes getting stuck for tens of seconds as every process on the system was contending on a single disk pagefaulting as they execute code.

I don't think that's correct. Having swap still allows you to page out rarely-used pages from RAM, and letting that RAM be used for things that positively impact performance, like caching actually used filesystem objects. Pages that are backed by disk (e.g. files) don't need that, but anonymous memory that e.g. has only been touched once and then never even read afterwards should have a place to go as well. Also, without swap space you have to write out file backed pages, instead of including anonymous memory in that choice.

For that reason, I always set up swap space.

Nowadays, some systems also have compression in the virtual memory layer, i.e. rarely used pages get compressed in RAM to use up less space there, without necessarily being paged out (= written to swap). Note that I don't know much about modern virtual memory and how exactly compression interacts with paging out.

It’s still beneficial so that unused data pages are evicted in favor of more disk cache