The standard BRIO switch is the curved switch track and it comes in two basic configurations: the traditional wooden track types L and M sold in pairs as #33346, and the mechanical switch track types L1 and M1 sold in pairs as #33344. The mechanical switches cost twice as much as the traditional track if bought new, but of course BRIO track can often be had for pennies on the dollar if bought used on eBay making the mechanical switches even more expensive by comparison. There are simply far fewer used mechanical switches for sale, either in lots or by themselves, where as the basic switching track is pretty much everywhere. So why buy mechanical switches when they cost so much more?
Well, the key advantage of a mechanical switch is that it prevents derailments. Unlike a traditional switch track, the mechanical piece guarantees that all the wheels in the carriage will follow the same path, and that all wagons in the train will do the same. With the classic track, some manual guidance is needed to ensure the train goes the correct direction, especially when negotiating the curved portion of the switch.
This is clearly important for battery trains, the whole point of which are to run without needing to be handled. But mechanical switches are useful even for unpowered engines, too. If you want to set up a layout where the default path through the switch is the curved path, not the straight, then a mechanical switch is going to be a lot more convenient and a lot less hassle than a traditional switch.
There are some down sides to mechanical switches, though. First, they are, as mentioned earlier, more expensive and harder to find used. Second, they take up more space. The mechanical actuator sticks out almost 30mm from the side of the track, so you can't lay the straight edge of a mechanical switch very close to a parallel run of track. And third, you have to be able to reach the actuator to move it.
With some careful planning, though, you can work around all of these. In general, it comes down to the following: use mechanical switches only where they are truly needed, and plan your layout so that there is room for them. In the coming days, I'll be updating the 2-D SketchUp model file to include the mechanical switch parts to help with that.