It should have no impact. It really is about write capacity. The little cells can only handle being changed so many times before they wear out. The wearing is a chemical/semi-conductor type problem.
It's not like DRAM where keeping power applied keeps the cells "fresh" (and in DRAM it's done literally be refreshing each cell at a certain frequency.)
The simple equation is the more times a cell is erased the sooner it fails. Write leveling and other software efforts work to spread around or eliminate unnecessary writes.
But over the practical life of a drive (5-10 years?) being powered off will not cause them to lose data.
Edit: I've been following FLASH technology since before the terms "FLASH" was coined, back when it was called EEPROM -- Electrically Erasable Programmable Read Only Memory, an evolution of PROMs (write once) and ERPOMS (erasable with UV light). If there's a myth out there that flash drives just forget things, I'd like to point out that I've had flash drives (low quality at that) from the 1990s that were left for 20 years and then read successfully! Show some citations of real evidence before you down vote me.