Have a SSD Drive and want to know why you need TRIM support on that drive?
It's because with TRIM support, it helps to scrub blocks of deleted data back into that current drive. Without it, your computer will think that the hard drive is full and that there is no more space to write on that drive.
If your buying an SSD Drive, make sure it's TRIM supported or that it contains wiper.exe to restore deleted data from your hard drive. If you don't buy an SSD Drive with these options, your going to have drive slow downs.
Windows 7 TRIM info