Different editions of the conference have taken their own approaches to running workshops as part of the proceedings.
Workshops are tricky because they require more planning, the tickets are harder to sell, and they're often more effective for smaller groups. It's also a challenge to get the right balance of topics appealing to developers of all levels of experience, and to find a venue that has appropriate spaces for concurrent workshops.
Still, they can definitely be useful to participants, and give organisers a day to ease into the running of the event. They also provide the opportunity to run Rails Girls and Rails Girls Next workshops alongside the others.
If you're going to have workshops, it's recommended that you have a CFP process that is either combined with the normal CFP, or runs on the same timeframe. As well as making communication easier, it lets your proposals team keep in mind any overlap between possible speakers and possible workshop presenters, and that may help guide the final decisions.