Ask HN: Are the any personal benefits in time tracking on your daily work?

I was really surprised today. We used to pay everyone in the company based on hours worked. Today we decided to replace pay-per-hour salary to stable monthly salary, but many people don't want to do that shift.

There is no overtimes in our company, we don't estimate user stories and as a company there are no reasons to keep time tracking. But people liked the flexibility. The arguments are:

1. I can work less and earn less, but it is OK with me. With fixed salary I will feel bad when I work less.

2. I can came over the weekend and earn some extra money (but in fact it is very rare).

Do you think pay-per-hour increase motivation?