High quality SSD drives support, and benefit from, TRIM.
That doesn't mean it is necessary. It is a "nice to have" if your flash controller isn't crap. Since they already implemented it in previous implementation most newer controllers just keep it around. Any current controller that solely depends upon TRIM is using it as a crutch and are just being lazy and/or cheap.
Garbage collection lets the drive guess about unused space.
Total BS. Any decent GC algorithm is not guessing. It either identifies garbage or it doesn't. Attributing this to guessing is spewing nonsense.
If it were really guess then sometimes it would collect non garbage.
When weaved into the wear leveaing attribute the GC algorithm knows with certainity that the old cell that used to have the data doeesn't. There is absolutely no guessing involved.
The only benefit of TRIM is when there hasn't been any wear leveling done in a while and need a set of "prepared cellls" that is bigger than the ones already queued up. That's it. So as long as the GC keeps the list of queued up cells long enough to satisfy the common data bursts it isn't necessary.
TRIM is also nice so that the drive as something to do when you are not using the drive. It providers more flexibitly to move the housecleaning can be timeshifted.
Given higher density MLC cells wear out faster than wider, old stuff there is no reason why the the wear leveling shouldn't be actively moving stuff around under the covers.
Garbage collection isn't bad, but TRIM is better.
TRIM isn't necessarily always better. The TRIM commands have to be sent down to the drive. That means the drive cannot be getting read/write requests. "better" perhaps in that it gives the GC algorithm a bigger window to get work down but at the core it isn't.
The information that TRIM provides is eventually propagated to the drive. When the file system starts reusues those freed blocks the drive will find out. TRIM advantage is that the info is perhaps communicated sooner. It is not that the information isn't communicated at all.
TRIM *and* garbage collection is best.
Yes but you are twisted about which one of those are more critical.