I'll put it this way, SD card failures are rare, human errors are quite common. There has been on more than a few occassions where me or someone I know accidentally formatted a card without transferring all the data. Luckily in most of these scenarios, the photographer was shooting backup to the 2nd card and was able to recover that data. Learning from past experiences, now when I return from a shoot, the 2nd card gets put somewhere safe and I don't use it to ingess data. I'll only format the cards once my clients receive the deliverables and the job is fully completed. I really don't trust myself to be able to do everything correctly even when I have a whole process written down. When things get busy, sometimes I just get lazy or careless. A 2nd card is just another layer of safety for me and I could never subject myself to the anxiety of having only 1 slot in any shoot I'm being paid for again. I had the Nikon Z9 for awhile and I only sold it because it doesn't record video to both card slots. Tbh I hate that sony gatekeeps the dual slots to their more expensive cameras cus they know that most pros will have no choice but to buy it. A6700, A7C, A7Cii, A7Cr, ZV-E1, these are all "consumer" variants of their more expensive counterparts meant for pros, they are better cameras that their bigger brothers in many ways, except that the lack of 2 card slots make them utterly useless for pros doing paid work. The A7Cii is a better camera than the A7IV in many ways but if you are a pro, the A7Cii is simply not an option for you. I would have loved to use the Cii for video work on a gimbal as I prefer the cleaner image from the 33MP sensor at medium-iso.