Do we cap the number of seats, or charge per active user?

I've been pricing by seats since day one, and I'm starting to suspect it's the wrong unit entirely.

Seats are simple. Everyone understands them, the math is obvious, and it scales naturally as a team grows. But seats punish exactly the behavior I want to encourage — sharing the product, inviting teammates, making it part of how a team works. Every person someone adds is another line on the invoice, so people quietly share logins instead of adding seats, and I end up with a customer who's deeply embedded but paying for two people.

Usage-based pricing is the opposite bet. Charge for what they actually use, and the product can spread freely through a company without anyone worrying about cost. But then revenue becomes unpredictable, people get anxious about a bill they can't forecast, and I get angry emails about a spike caused by one busy week.

I've watched companies switch from seats to usage and grow faster. I've also watched usage-based pricing terrify buyers into choosing a competitor with a flat number.

Which unit do you charge on — seats, usage, or something else? And did you ever switch, or just inherit the model and never question it?