TRIM is a special ATA command which was developed to keep the performance of your SSD drives at peak performance for the duration of your SSD's life. TRIM tells the SSD controller to erase invalid and not used data blocks from the storage in advance, so when a write operation happens, it finishes faster because no time is spent in erase operations. Without TRIM automatically working at the system level, your SSD performance will degrade over time unless you manually use a tool which can send the TRIM command to it.