I am a photographer and work extensively all over town and in the studio and do not have much time to do other things. I started using Payday when I started working as a freelancer. I just needed a simple system that worked well and this just solved all the problems right away.
Payday a great time saver for people who are always out working like in my case. I've been using Payday because I like this clever solution. I saw a great advantage of being able to just send invoices directly from my phone. It is such a great feeling to have all things in one place - let alone in your pocket.