Traditionally, subterranean termites (the kind we have in the Phildelphia area) have always been treated with chemicals injected into the ground around the entire perimeter of a home. The exterminators drill every 12-18 inches both inside and outside to create a chemical barrier. This method, usually is immediately effective at killing termites and stopping them in their tracks. Occasionally, there are gaps in the barrier and re-infestations need to be retreated, but this is not terribly common.
Then, someone came up with the idea of "bait stations" and they are being heavily marketed by the large franchise termite companies. The theory is that small bait stations with wood in them are placed in various locations outside the property. The companies come back at quarterly intervals to "monitor" them. If they find termites in one of the stations, they then replace the piece of wood with some chemically impregnated wood. This is supposed to be taken back to the termite home under ground and then kill them.
I may be oversimplifying, but here is what I have observed in several properties I have sold that have these bait stations. While the termites are eating the wood in the bait stations, nothing is stopping them from eating the wood in your house! They just don't work and the termites continue to dine on your home leaving extensive wood damage if they go unchecked. Moreover, these bait stations are almost three times the initial cost as a traditional treatment and the annual contract to maintain them is about $400 per year as compared with about $100 per year for the traditional, and, in my opinion, more effective method.
They are promoted by companies for one reason - they are cash cows and great profit centers. So, if you find out you have termites in your home (usually you will see a swarm of insects in either the spring or fall that looks like flying ants)make sure to get all the facts before you decide on treatment and don't fall for the glossy sales pitch. Obtain several opinions from both small and large companies.
There are some situtaions where the bait stations are the only alternative, for example, in homes with well water as opposed to public water. As always, get informed to make the best decision.