Sometimes it feels like asking for too much, true.
Can also answer as a percentage of the drive's fullness. Joe Customer may say "the drive is 50% full", which could be very helpful.
Some users are fairly informed about their stuff, so it is more beneficial to ask, rather than assume they don't know and not ask.
It is a few seconds question & answer scenario that could help reduce head scratching, time wondering, and potentially getting upset committing to do a job for cheap while it could turn out to be much more difficult and time-consuming than initially anticipated. I see it all the time.
Actually, you do. The Synology finder software installs the OS to it when if first finds the NAS. That's what the Synology DSM you download is, it's the OS. It's just small and stored as an image file. So it installs pretty quickly compared to a bloated OS like Windows.