The iPad can be a very useful tool for working musicians. I use an iPad to run click and/or backing tracks at church. If I'm subbing with a group, I will use an iPad for set lists, song structure notes and lyrics for leads or harmonies. On some PA systems, you can control your own monitor mix as long as you have the app for that brand of console. I don't use it on many shows but when I do, it contains really any show related notes I could think to put in there and the wind or my fan isn't going to blow it off the stand.