Quick vs long format

[wraper]

Any drive which has been in use for a while will have no unused sectors beyond what TRIM indicates.

BS

This however is correct. At some point every flash page has been used once and only TRIM can mark some as truly empty again, and that point comes quickly since the drive will typically favor using empty pages first before starting to do read-modify-writes on partially full ones.

Any modern SSD has some reserved amount of storage above what is visible to OS. Also they have garbage collection. Though it does not work too well without TRIM. As it only deals with remaining data of physical blocks  where majority of their content was written to other physical blocks, no idea about deleted data. Thus moving a lot of garbage data around.

[wraper]

So tell me, why would a new SSD which has never been used report bad sectors?

Maybe because they were really bad/ drive was faulty? Why drive would mark them bad if it was simply a retention problem? Also you did not say how many bad sectors.

How do they work if the OS does not use TRIM?

Reserved area not visible to OS + working like slow crap after a while if there is no garbage collection implemented like in early SSD.

In practice the performance advantage of TRIM only becomes significant with drives which were poorly designed in the first place with insufficient reserve space.

In practice give or take erasing and then writing is very slow compared to simply writing. Without TRIM the only way do deal with that decently is either understanding file system or having large amount of reserved area. But you still will get writing amplification as any garbage collection without TRIM is still moving orphaned data = excessive NAND wear. The only data it knows to be really orphaned is which was written over by OS (written to another block internally). Also reserved area may fill real fast when you try writing large amount of data resulting in abysmal performance before garbage collection is given idle time to do it's job. It would be proper to say that garbage collection without TRIM is the real crutch.

[Jeroen3]

Then how did drives work before TRIM became available?  How do they work if the OS does not use TRIM?

Read-Erase-Write. On spinning disks there was no erase step*, just overwrite.
It's especially bad when the erase blocks are misaligned with filesystem allocation units.
The magic in an SSD is to only have write until all blocks are used.

https://www.micron.com/-/media/client/global/documents/products/technical-marketing-brief/client_vs_enterprise_performance_use_cases_tech_brief.pdf?la=en

^{*today we have SMR, it's crap.}