>and if you are shooting still (and not video) there's really no good reason to ever delete an image off an SD card
There are tons of good reasons.
When downloading images off the card, software has to read all the files on it - which can take a very long time if the card is full of photos you've already processed in a previous session.
Then there's that you shouldn't be keeping most of the shots you take. Unless you're a still life artiste, most people (including professionals) take multiple pictures to account for blinking, moving objects, slightly different angles, etc. You should keep the best shots and delete the rest - storage is cheap but having to go back through all the garbage to find the good shots in the future is pointless.
Modern cameras have large sensors that produce large files. It's wasteful to keep buying more and more SSD cards. Just build a NAS or pay for cloud storage.
It doesn't avoid the delays. I have incredibly fast CFx cards, an incredibly fast card reader, and an incredibly fast CPU in my desktop, but the simple reality is that reading tens (or hundreds) of gigabytes over USB takes a long time, and analyzing those files to determine if they're already in my large photo library takes a lot of resources too. Minutes, not milliseconds.
A RAW file from a Nikon Z8 is generally 50-70MB. If I left 300 photos on the card before going out for a shoot, that's tens of gigabytes of data to transfer and analyze before the software can get to the images I'm actually interested in. If it's hundreds of gigabytes the problem is even worse.
Then we can go the other direction. Popping a partially full card in my camera with media that I can’t sort through at a glance/quickly. Library software isn’t going to help you there.
Best practice is to dump, back up, and format. If you’re doing photos and you’re not shooting several gigs per shot hundreds of times then sure you can hold onto those SD cards, but then you need to take them out of rotation.
Ultimately boils down to the kind of user we are talking about, which is incredibly varied
There are tons of good reasons.
When downloading images off the card, software has to read all the files on it - which can take a very long time if the card is full of photos you've already processed in a previous session.
Then there's that you shouldn't be keeping most of the shots you take. Unless you're a still life artiste, most people (including professionals) take multiple pictures to account for blinking, moving objects, slightly different angles, etc. You should keep the best shots and delete the rest - storage is cheap but having to go back through all the garbage to find the good shots in the future is pointless.
Modern cameras have large sensors that produce large files. It's wasteful to keep buying more and more SSD cards. Just build a NAS or pay for cloud storage.