What is Trim?
Every time you delete a file on your computer, the data still stays on the drive in segments called blocks. These blocks are not deleted until you need to use them again to write new data. Due to technical limitations in the NAND Flash design, only whole blocks can be deleted. This means that when you need to write new data, the SSD must perform time-consuming cleaning and maintenance of these blocks before your data is written. With Trim, your blocks can be cleaned instantly when you delete the data, leading to much less operations during the writing process which gives you better speeds and minimizes the wear on the drive.
Still don't get it?
Then don't worry, Just treat Trim as your garbage collector. When your bin is full, your bin man will come and throw all the garbage away. That is what Trim does. Without Trim, your bin man will just shift your garbage from the dumpster to one side and continue letting you dump more garbage into the now empty bin. When the bin man no longer no longer has space to shift the garbage, he will take a lot of time to dump all the garbage collected into his dumptruck. Which do you prefer?
It seems like the new Yosemite OSX is making it difficult for hardware vendors to implement Trim in their devices to work with the proprietary driver. Refer to Cindori Trim Enabler for more info. I personally don't feel the need to enable Trim as i do not mind the negligible speed difference and i am sure my MBP will last me probably for another 2 years tops (my new SSD should be able to last that long too), so will ignore the additional workload on my SSD. Comon, i bought you to work for me you piece of hardware! :P
The only way to allow TRIM to work with third-party drives under Yosemite is to disable kext signing.
For people who wants to enable Trim, please think twice as the security hole is bigger than you thought.