If you are asking the question, you are relatively new in the profession. So, for you the answer is: PBS will make your life hell. Since it favors seniority above all else.

PBS only allows senior people to more effectively manage their time. There are a few ways they can do it, the most common at the regional level seems to be specifying what days you want off, and what type of trips your want, and what cities you want to layover in... basically the most senior person on the list tells them what he/she wants. They give it to him/her. Then the next person goes... by the time it gets to the middle of the seniority list.... there are only a few getting weekends off, and all of the trips have long sits... by the time it gets to junior people... all are working weekends, on long four day trips with long sits between each leg, or day trips that do two legs in a 16 hour duty day.

Does that help explain it for you? It's another case of senior people eating their young. Just about all senior, and most mid level folks will do better or at least the same with PBS, and since majority rules... the bottom one third of the seniority list suffer and pay the price...

kinda like pay.... the top 1/3 makes out while the bottom 2/3rd's pay for it.