The Flyers will start the season in Europe and will conclude preseason with an exhibition game against a Swiss team. The CBA actually outlines the minimum amount of veterans you need to dress per preseason game, so adding somebody like Stewart gives you a little flexibility. Especially for the older vets who you know will make the team, you can spare them a roundtrip flight for a meaningless game earlier in preseason.
LA/Vancouver played in China a couple years ago and primarily sent their A-teams, but I think they had other preseason games concurrently in North America so they signed some flotsam on PTOs to dress for the B-teams.
I know it's the usual reaction to react to a PTO as if it's a guaranteed contract, but most of these guys won't get signed. If anything, they'll be future entries for the "What are you doing wearing that uniform" thread. I still remember going to a Devils preseason game where they had Tomas Kaberle and Mike Komisarek on the blue line.