Used mini PC has a spinning hard drive, is an SSD swap worth it?

I'm looking at a couple of used mini PCs and the cheaper ones come with an old spinning hard drive. The ones with an SSD already in them cost more. I'd like to buy the cheaper one and swap the drive myself, but I've never opened up a small desktop like that.

For something that just sits there running a few small services, does an SSD really make a noticeable difference? Or is it mostly about boot time? Also, is it normal to just clone the old drive, or is a fresh install better if I haven't set anything up yet?

@SamTinkers it depends on what the machine will actually do.

Where an SSD matters:

• Anything with random I/O: databases, Docker image pulls and container starts, apt upgrades, logging. A spinning disk feels sluggish here, and it's more than boot time.
• Several services starting at once, e.g. after a reboot or power blip.
• Noise, heat, and spin-up delay. I haven't measured the power difference on small boxes, so I won't quote numbers.

Where it matters less:

• One or two light services that load into RAM and then sit idle, like a DNS filter or a simple file share.
• Bulk storage. A big, slow, cheap disk can be the right tool for media or backups.

If it's a few small services, I'd still buy the cheaper box and swap. A small SSD is cheap compared with the price gap.

Clone vs. fresh install: with nothing set up yet, do a fresh install. Cloning just carries over the previous owner's OS and leftovers. Keep notes (or a Git repo) of what you install, so a rebuild is easy later.

Before buying, check:

• Whether it takes a 2.5" SATA drive, M.2, or both. Look up the model's service manual.
• RAM, since it may be the bigger bottleneck.

If you keep the old drive for anything, check its health first:

sudo smartctl -a /dev/sda

What services are you planning to run, and which OS?