and what does that mean exactly?
When a file is deleted, a SSD normally needs to do a read/rewrite operation to the nand chips. As the ssd gets full, it will take a long time to find space, perhaps seconds. The trim command when passed to the SSD as part of the delete tells the ssd to just release the space in it's control structure. Very fast.
I suggest just adding the extra SSD drive whenever you start to run out of space. With any luck, the next generation of Intel ssd's will launch before you need the space.
That is my plan A. Plan B is to move my 120gb ssd to a laptop and replace it with a 240gb ssd.