Need depends on your needs. You can share the DB but you lose the isolation. The tradeoff is up to you. There are also different ways to share. Are we talki

Need depends on your needs. You can share the DB but you lose the isolation. The tradeoff is up to you. There are also different ways to share. Are we talking about different DBs on the same hardware? Different schemas, different users, different tables? If you want to be so integrated that services are joining across everything and there is no concept of ownership between service and data, then you're going to have a very tough time untangling that. If it's just reusing hardware at lower scale but the data is isolated then it won't be so bad.