Dan makes great points, but the reason I say especially at a smaller company is that you have less to manage. It's easier to set service accounts for a dozen or so instances.

At a larger company, imagine 1000 instances. It becomes a chore if you deploy instances at any scale. We had hundreds (300-400) at one place I worked, and we had separate accounts, but developers, Windows admins, etc. constantly complained. Getting new accounts, setting things up, was a small issue (to me), but it felt large (to some people).

I typically use a long, 25char, one time password for service accounts. Someone creates the account, writes down the password (no digital trails), we enter it in on setup (or later) and then we destroy the paper. If we need to get to the service account, we just change the password.