Taken from http://forum.crucial.com/t5/Crucial-SSDs/TRIM-and-SSD-performance-why-is-it-important/ta-p/100276
Recently we’ve received multiple calls about the TRIM feature and how it relates to Crucial SSDs. In a nutshell, TRIM is a feature that helps increase the efficiency of your SSD by preparing data blocks for reuse. Here’s how it works.
TRIM and Data Blocks
On hard drives and SSDs, data is stored in blocks (“data blocks”). Each data block has data from more than one file, and on a hard drive the blocks can be split whenever necessary. When you delete a file in your operating system, for example, the hard drive deletes only that specific file’s information from the data block, leaving the rest in place. When a file is deleted in the computer’s file system, the data stays on the block until the next time that block is needed. At that point the drive swiftly deletes that particular piece of data from that part of the block, and writes the new file there. Essentially, hard drives are able to delete information from part of a data block – they don’t have to delete the whole thing.
In contrast, SSDs have to delete an entire data block before they’re able to reuse it. As such, when an SSD is trying to clear a data block, it puts a copy of everything on the block into a cache (“holding place”) and makes the necessary changes there. The SSD then deletes all of the data on the original block and writes the new data that it was trying to write in the first place.
Understandably, going through all these steps takes a lot longer than it would have taken to simply write data to an empty block. Since the SSD knows this, it simply locates an empty block and writes there. This works great – as long as empty blocks are still available on the drive. When all of the blocks are filled up, the SSD has no choice but to start deleting blocks and reusing them, resulting in a drop in write speeds. This problem, however, can be overcome with TRIM – a feature that prompts the SSD to clear previously used data blocks. With TRIM, the next time an SSD’s filing system wants to write to those blocks, they are already empty and ready for use.
And now the the part specific to Crucial SSD's...
Crucial SSDs and TRIM/Garbage Collection
Since not all operating systems support TRIM, Crucial SSDs have a special feature called Active Garbage Collection. Active Garbage Collection is a process that helps an SSD maintain optimal performance by freeing up memory sectors that are no longer in use. Garbage collection is part of the SSD itself and thus not dependent on your computer’s operating system. Since garbage collection is part of the SSD’s firmware, it works regardless of which operating and filing systems your computer is using.
Note: Garbage collection only works when your Crucial SSD is idle, so make sure to configure your system so it doesn’t go to sleep when it’s idling. Garbage Collection takes time to do its job, but as long as it gets time to idle every now and then, your Crucial SSD will maintain its high level of performance over time.
It's possible other manufacturers do something similar.
In a nutshell, I would say that manufacturers have already responded to performance issues using built-in functionality that requires no OS intervention. In which case, unless you're running a server or have little empty space left for example, TRIM isn't an issue.