Apple has implemented TRIM support on third-party Solid State Drives in OS X 10.10.4, without the need to utilize workarounds or extra software. The move sees Apple expand TRIM support beyond SSDs shipped with Macs, better optimizing hard drives used with OS X, even those bought aftermarket.
The new TRIM support enables the OS to enhance file cleanup operations on the attached SSD to keep the system optimized and running without issue. A SSD works differently from how a traditional spinning drive handles data removal. Since storage mediums in general have no knowledge of the file system structures, including the list of unused blocks and sectors, hard drives remain unaware that free space has become available.
This is how you're able to recover data using software on spinning hard drives. But for SSDs this means that when the OS comes to write to that specific block, which is considered to be free space by the OS, the task becomes an overwrite operation, which is where SSDs can suffer slightly, while magnetic hard drives are able to overwrite as if they're pouring data into an empty sector.
Some SSDs may show signs of crippled write performance should the drive be performing overwrite operations, which is where TRIM comes in. This command essentially allows the OS to inform the SSD which blocks are no longer required and the storage medium will perform appropriate cleanup operations. This helps prevent dips in performance when writing to the SSD.
It'll be a welcomed addition by many, we're sure.
Source: Apple Insider