Every artist places a different emphasis on rehearsals. On one end of the spectrum, the Shakira organization has been known to rehearse for up to three months before a big tour. There are so many details to cover. First, we put a band together, and we rehearse both old and new material. A few of the songs from the previous tours may need new arrangements to surprise the fans.
After the band works up all of the music, Shakira comes in to begin singing with the band. Then, the choreographers arrive to start working on the dance moves to go along with the new arrangements. Next, the monitor and front of house engineers, and the video and lighting guys come in to work on the sound and visuals. It takes a while to put a show like that together. On the other hand, I have worked with artists who keep the rehearsing and production aspects to a bare minimum. Just show up and play!