My camera has built-in wifi, so not sure if it's the same experience as a wifi card.
But I love the wifi feature and wouldn't consider buying a camera without it. It's great for sharing a few of your best photos taken with your best camera. I know you could do that with a phone camera, but much of the fun of photography is using a fine, capable camera with carefully chosen lenses & putting thought into the composition. With camera wifi, you can retain that aspect of photography & still have some of the immediacy of sharing your pictures with friends & family via phone. Best of both worlds. It only takes a minute to transfer 1-3 pictures to my phone (maybe not even that long? I've never timed it.)
Sometimes when I travel I'll wifi my best pictures to my tablet. I can then crop & post process if desired, & now I've got a nice means of display via the tablet to enjoy the fruits of my photographic day.
I hate taking pictures with my phone, frankly. Options are too limited, poor image quality, awful shutter lag. Takes crummy pictures of the grandbabies -- not worth showing to my friends.
Don't think you'll be able to upload a whole day's shoot, though -- too slow for that.
ETA: just reread your post & realized this doesn't answer your question -- is wifi more useful beyond sending photos to a phone for sharing. Perhaps uploading to a tablet for editing & display is marginally more useful. Still, camera to phone/tablet connectivity for small batches of files is at the very least a wonderful convenience.