Always - it worked really well. On the one occasion in our 8 week Camino that it didn't arrive (when a hotel staffer offered to call the transport for us and forgot!), the Jacotrans driver was brilliant and actually went back and picked it up for us on his next run. Of course, you do need to have a destination, so you really have to book accommodation ahead if using these services, so they have somewhere to deliver to. That wasn't a problem for us, we wanted that certainty, but it might not suit someone who prefers not to book ahead. All the accommodation providers were very familiar with the system (we used a combination of private albergues and small hotels/pensions/casas rurales) - it is very well-used right along the Camino - and they would have the envelopes to leave with payment, tell us where to leave our bag for collection and/or offer to book for us (I usually booked a few days ahead online, but you can just call the night before). Once we were within the last 100km we often didn't even need to call the transport services, as they just turned up anyway. I would definitely do it this way again - as I said, for us it made all the difference, as it allowed us to walk the Camino.