TRIM is the command that lets an operating system tell an SSD which blocks of data are no longer in use and can be wiped, preparing them for the next write. Without this, the process of reading, deleting, or moving data can slow down as the SSD maintains information that is no longer used. Unfortunately, Apple only enables TRIM on its own drives, in a move to perhaps discourage customers from going the aftermarket route. Fortunately, the restriction isn't hardwired. There's a bit of terminal window work to lift the Apple SSD requirement, but it's all covered in sufficient depth at Github.
Be forewarned that there are programs out there written to enable TRIM support with a single click. They're often unreliable, though, and some are even outdated, compatible only with Snow Leopard or earlier versions of OS X. If you want to do this right, follow the instructions linked above.
Note also that OWC's official party line is that you do not need to enable TRIM on the Aura Pro due to SandForce's DuraWrite technology. The reasoning behind this is that DuraWrite frees up space on the drive that can be used for garbage collection, similar to what TRIM already does. The rub is that DuraWrite requires compressible data to operate on. In a typical use case, you're going to have some information that can be compressed. But if you're dealing with exclusively incompressible data, DuraWrite won't help, and you're going to be missing TRIM support. For that reason, we're enabling it. Check out this presentation by LSI's Kent Smith at the Flash Memory Summit in 2011 for more (specifically, slide seven).