There's plenty of disagreement about TRIM and a fair amount of confusion too. A long TRIM explanation is here which goes beyond just TRIM but is still good to know. In a nutshell, HD's and SSD's don't work the same way. With a HD, if a file is deleted, that space is immediately available for reuse without any further action needed. With an SSD, the space needs to be erased before it can be reused, and while only a page of data may have been deleted, only a block of many pages can be erased. Since some of the pages in the block may still contain valid data, those pages have to be moved elsewhere before the erasure can take place. But when a file is deleted, the operating system knows about it but the SSD controller doesn't, so invalid data gets moved too. TRIM is the method by which the OS notifies the SSD controller of the deletion. The link I included regarding Garbage Collection and TRIM explains how GC can get by without TRIM. But activating TRIM is, in most cases, beneficial. How beneficial is best demonstrated in the graphs showing test results for TRIM activation.
While TRIM can be activated for third party SSD's, Yosemite introduced a complication. While TRIM can be temporarily deactivated in instances where it would interfere with things like OS updates, there may be times when you can't or forget to be proactive. So there's no easy answer.
