Apple is starting to add SSDs to the MacBook Pro line and eventually its desktop Macs to improve battery life and shorten boot up times. However, Snow Leopard can’t optimally handle the drives. All versions of OS X treat SSDs as a Hard Disk Drive when deleting a file or formating the drive. SSDs function differently than HDDs and must erase data before new data can be written. HDDs on the other hand can write data over old data without the need to erase.
Treating a SSD in this way will degrade performance over time as the drive’s flash cells are unnecessarily taxed and will wear out after a certain amount of read/write cycles. TRIM doesn’t wear out SSDs and deletes data in a far more efficient way. Apple has implemented TRIM support in the newest developer preview of OS X Lion but is limited to drives Apple has shipped with a Mac. TRIM support means the SSD in a MacBook Air can last longer and won’t ear out due to unnecessary data erase commands.