If you have the option to bill on a daily increment, why would you ever bill hourly?
There are some circumstances where I think this can make sense.
One is that for urgent, very short, very specialised gigs (for example, an emergency fix for a previous but not usually recurring client) you might command a much higher rate per hour than the equivalent of your normal daily rate for medium-long term gigs. This just follows from all the same reasons we've talked about on HN before in terms of business value generated vs. time served.
Another is that it is sometimes useful to multiplex a part-time contract gig with some other task -- another part-time client, a start-up, supervising the guys building your home extension. It can be advantageous for all concerned to be up-front about the fact that you're only working part-time and how much time may vary considerably from day to day. This manages expectations if, for example, you aren't going to be around to answer the phone at reliable times. Obviously really top-end consultancy work isn't likely to be forgiving of part-time engagement anyway, but you probably aren't attracting that kind of gig no matter how good you are while you're also working part time on something else that can't wait.
There are some circumstances where I think this can make sense.
One is that for urgent, very short, very specialised gigs (for example, an emergency fix for a previous but not usually recurring client) you might command a much higher rate per hour than the equivalent of your normal daily rate for medium-long term gigs. This just follows from all the same reasons we've talked about on HN before in terms of business value generated vs. time served.
Another is that it is sometimes useful to multiplex a part-time contract gig with some other task -- another part-time client, a start-up, supervising the guys building your home extension. It can be advantageous for all concerned to be up-front about the fact that you're only working part-time and how much time may vary considerably from day to day. This manages expectations if, for example, you aren't going to be around to answer the phone at reliable times. Obviously really top-end consultancy work isn't likely to be forgiving of part-time engagement anyway, but you probably aren't attracting that kind of gig no matter how good you are while you're also working part time on something else that can't wait.