Yes, you can have several company profiles. If you manage several companies, you will appreciate that a single login is enough. You can have any number of profiles under one account, each for a different company, and switch between them as needed.
You can also invite users across company profiles, and the same user can have a different role in each profile. For example, in company A they can act as an Admin with full access, while in company B's profile they only have the Support role and, say, process payment refunds.
You switch between profiles in the top right corner of the interface. Just click your name or e-mail and, in the expanded menu, select the one you want to go to in the Other profiles part. You do not have to log out or log in again.
The number of profiles is not limited in any way. The interface also always remembers the last profile you had open, so when you log out and log in later, you continue exactly where you left off.