This should be a question to google; since this has only been explained a few million times before. ;-)
TRIM gives some space that you do not use to the SSD, which uses it to keep its performance-level on par.
Without TRIM-capability, your performance might drop, sometimes considerably, below its factory performance levels.
You need either Windows 7, Linux or FreeBSD to use TRIM. Older Windows releases and Mac OSX do not support it.