You are a wise man to think of this and ask. As of the latest firmware update (2.4.1-6), that parameter no longer applies only to auto mode on the Pixhawk. That now affects auto and guided mode. All the smart shots use guided mode. So if you program a smart shot that takes the Solo out of range, or your controller craps out on you in the middle of the shot, it will continue with the shot as programmed. This can be very handy if you're doing something like an orbit around an obstruction where you lose signal temporarily.
However, you must use this wisely and understand the implications. For example, you setup a zipline, push the play button, and it starts moving along the line. The very nature of zipline means it will keep going along an infinite course. With that parameter set, it can now keep going beyond the range of the controller. It will just keep going until the battery reaches failsafe level. At which point, it probably won't have enough juice to make it home, and will crash on the way back. Another scenario, is you're doing basically any other smart shot and the controller dies. In the case of a MPCC, it will proceed to the end, then just sit there until the battery failsafe kicks in. With an orbit smart shot, it will just keep orbiting around and around until the battery failsafe kicks in.
So, use it but use it wisely.