Dogs show up inconsistently at BDL. They’re not there every time and their presence is unrelated to other steps in the TSA security process (i.e. the rest of the process isn’t simplified when the dogs are there). Most of it is they are sniffing for explosives and “other contraband” which is usually drugs and large amounts of cash, which while it’s legal to fly with a large amount of cash, the government may try to find ways to claim it.