Startup time is usually a lot slower, as are database updates after installing a software update.
Importing new content is much slower. Applying edits to the database, especially larger operations like bulk editing or changing library settings can be miserable. Re-identification or re-scan of files is slower. Background metadata updates are much slower. Many of these operations result not only in the operations taking much longer, but also general slowness that effects Roon as a whole while they are happening.
Also, while browsing, images will load more slowly into the user interface, and many page loads which touch the disk will either take longer to show up or exhibit variable latency.
We look at SSDs as an enabling technology for software like Roon. We don’t perform QA testing with spinning drives because we’ve treated SSD as a system requirement since day 1. If someone with a spinning drive shows up complaining about performance, it’s the first thing we ask them to address.
If it’s working for you, that’s fine–just want to paint an accurate picture. I wouldn’t want to use Roon in a non-SSD configuration, but only you know what is best for your situation.