Apple’s argument for getting rid of the SD slot was that the future would be wireless, and we wouldn’t need to use cards to transfer data anymore. It wasn’t true back in 2016, and it’s still not true. Sure, some devices equipped with SD cards now offer wireless data transfer, but let me tell you—it’s not as fast or reliable as just plugging in a card and transferring the data! And a lot of our non-Apple devices still rely on slow USB ports to transfer data if you have to copy the data directly. The SD slot is just convenient whether you’re a pro transferring photos, audio, or video.
Apple markets their pro machines specifically at creatives who use cameras and recorders that use SD cards for everything. In 2016 the argument was that these devices would move to USB-C or wireless connections for transferring things to your computer, but that has only sort of come to pass.
Most high end cameras can wirelessly connect to your computer (or phone for that matter), but they often transfer super slowly, and sometimes even convert your RAW images to JPG in the process (presumably to improve the transfer speed). Wired connections work, but often transfer speeds are still very slow due to slower USB tech in the device. Using my Canon EOS RP as an example, I can plug in via a USB-C cable, but photos and video transfer at about 1/3 the speed I get from just plugging the SD card into Apple’s SD-to-USB-C adapter.
Another issue is that many photographers shoot with multiple SD cards. If they have a big job, they’re going to have several SD cards with them, and they’ll swap between them as they fill up each card. Needing to use their camera as a several thousand dollar dongle to offload these photos/video to their computer is a pain (and has slower speeds).
Not everyone will use the SD card reader in the new MacBook Pros, but I for one am so happy to see it come back.