That's a good question. I would think that at home, if you keep the humidity under control, you wouldn't need it there. In route to a gig, if you have the air conditioning on, the air is probably keeping the humidity down and it may not be necessary there. At the gig of course the bass is going to be out of the case so it's not going to help there. Of course, at home, it's not always so easy keeping the humidity under control. If your house tends to get humid and you don't have a dehumidifier and you keep your bass in its case, then maybe it's a good idea to keep a fresh silica gel in the case.
