@Switch BlaydeRight now my wife has Time Machine scheduling a full backup every hour. That's a lot of writing to the backup drive. I'm trying to convince her that's overkill, but we'll see.
As others have pointed out, only any data that has changed in that period will be backed up.
If the backup is configured correctly, things like the internet cache & temporary files won't be backed up- only system updates (if any occurred during that period) and whatever files were being actively worked on. ie email (if locally stored), word processing, video or photo files being edited etc.
There is only one reason to buy a HDD these days- capacity. If you need more than 2TB of storage then a HDD is the way to go. If you need 2TB of storage, and can't afford a SSD, still buy the SSD. If you really can't afford the SSD then get the fastest HDD you can. Anything less than 2TB- don't consider anything other than a SSD.
A HDD that is low on free space runs like a 1 legged dog, so too an SSD (and it will hasten it's end of life). Make sure to buy a drive that will have at least 40% free space after 5 or so years of use.
As for writing killing an SSD- yes, they do have a limited number of writes before they die. And when they die, they (should) become write only- they can still be read from. But it's not unheard of them to no longer be readable. In some case not even detectable by the OS or even hardware.
But the fact is it takes a lot of writing to kill even the cheapest of SSDs. As in a stupidly massive amount, every day, day after day, for months on end. Drives are rated in the number of drive writes per day they can sustain as a fraction of their capacity. Even the most basic drives can handle 0.3 DWPD (30% of their rated capacity, every day, day after day) to their rated limit (generally in the hundreds of Terrabytes written).
A tech website did a test on several different SSDs to see just what it would take for them to fail, and how long it would take. It took 18 months for the last drive to finally die. These were generally available consumer drives, not high endurance enterprise drives. And they did this 5 years ago. Even though TLC drives are now the standard, wear levelling algorithms have progressed quite a bit over the least 5 years as have the manufacturing processes & the results today would be similar, if not even better.
Some drives were rated for 20TBW, none died till after they had gone well over 600TBW. The winner made it to 2.4PB after 18 months of abuse before it died.
https://techreport.com/review/27909/the-ssd-endurance-experiment-theyre-all-dead/