I worked for a company that did this, we had hundreds of database instances, one per customer (which was then used by each of those customers' employees). It w

I worked for a company that did this, we had hundreds of database instances, one per customer (which was then used by each of those customers' employees). It worked out pretty well. The only downside was that analytics/cross customer stats were kind of a pain. The customers all seemed to like that their data was separate from everyone else's. This never happened, but if one database was compromised, everyone else's would have been fine. If I were starting a B2B SaaS today where no customers shared data (each customer = a whole other company) I would use this approach.