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If you have a drive with 10k writes,  and you have a mechanism in place that prevents mostly needless rewriting of the data from happening,  organizing it into a minimum number of operations instead, then you have effectively increased the lifespan of the product for the consumer.

I’m not claiming to be an expert either, but that is my interpretation of how TRIM is supposed to work.

I’ve done some more reading….

I think we are both correct to a degree..   TRIM tells the SSD controller which pages have been deleted, and allows the SSD to wipe out those pages only – I think its fair to say an SSD without TRIM support would reach its write-cycle limits much sooner than a drive utilizing TRIM.    Likewise, it would also help maintain performance as there is no  hit from the erase/re-write operation.

TRIM, garbage-collection, Intel SSD Optimizer ~ they all are about maintaining performance over the lifespan of the SSD not about increasing the lifespan itself. My personal take on their impact on lifespan is explained in the previous comment.

If someone is an expert and/or has reliable sources that state otherwise I’ll gladly admit having been wrong.

This works perfectly up to the point where no empty blocks are available anymore. At that point each and every write operating is delayed by the block level erase and drastically decreases the performance of the SSD ~ this is why garbage-collection and later on TRIM were implemented.

The white paper on TRIM nowhere states that it is supposed to maintain a longer lifespan. Like Garbage Collection it is supposed to maintain (write) performance of the drive.
White Paper from Supertalent
Intel SSD Optimizer

Garbage-collection is an (sometimes automated) program that scans and erases blocks containing deleted data
TRIM is an command set that tells the SSD to erase data from blocks as soon as the file is deleted (moving the pages, erasing the block, and writing remaining pages on firmware and cache level)

As stated above (and mentioned here and here) MLC and SLC do have a limited amount write-erase cycles. 
Without TRIM or garbage collection each block of the SSD would have to be used once before the first write-erase cycle appears.
With those technologies pages are going to be erased and empty regularly (available for new data) which leads to some blocks going through multiple write-erase cycles while others might have never been used. This obviously results in some of the blocks having a shorter or actually faster reached lifespan than others ~ faster than it would be without those features.

//edited the last part to make it easier to comprehend

Everything I have ever read has stated TRIM is used to help maintain a longer lifespan on the drive, by the OS telling the drive that sections which held data, are now invalid due to a user or the OS deleting something.   This prevents the drive from writing new data during garbage collection operations.

You can only delete data on SSD’s in blocks currently,  which means even though you can do  page-based write operations (a block has many pages) the ENTIRE block still needs to be erased and rewritten.   Thus the block has to be cached to memory,  the block erased, and the block written back with the modifications.   It is called write amplification and can drastically reduce the lifespan of SSD’s because of the limited  Read/Write cycles we currently have.

Depending on how TRIM is implemented, it can help maintain performance as well (its faster to write to a empty blocks than to erase/rewrite) .  But TRIM is certainly not going to help kill a drive; it was designed to do the exact opposite.

Some things should be disabled,  such as  Defragmenting schedules (there is no need to defrag an SSD, especially with TRIM enabled drives),  Indexing on the drive (I turn it off completely, its useless to me anyway).

You should also store all temporary files, including your Windows SWAP File, on mechanical drives.   Temporary data by nature changes fast,  so why would you expect your SSD to live that long if Windows is always using  the SWAP file, or writing/deleting temp files for installs, uninstalls, and other actions?  Not to mention web browser’s using their storage cache.

All that stuff should be left on a mechanical drive.

in case you don’t get a reply here, I suggest to ask this question over at MakeUseOf Answers.

I am looking to get a new iMac actually – does anybody here know whether Apple install their OS on the SSDs (where you can upgrade to have an SSD as well as a HDD)?

The first SSDs on the market used RAM memory (and similar) which made them very expensive. On the other hand RAM was obviously made for massive read & write operations.
Current (inexpensive) SSDs are mostly based on rather cheap MLC Flash memory which have an average life of 10.000 program-erase cycles. That’s not much on it’s own.

What added to this is the growing support of TRIM which helps in keeping the SSD performance on a high level. The function tells the SSDs firmware to erase not used blocks – basically you trade speed for lifetime.

The expensive SSDs (targeted for enterprise) for example are based on SLC Flash memory which endure about 100.000 cycles.