I see. It makes sense for short-term-ish projects.

But I had experience of long-term working with the client, where there are no milestones. There is just an unlimited continuous flow of work to be done. So if you charge daily, that most likely implies 8 hours of work per day. Basically, it is more like a regular employment, but with a freedom of working whatever hours you want, including zero.

I was just summing up the worked hours at the end of the month and billed with it.