Thunderbolt 3 is backwards compatible with USB-C, and uses the same connector. Both are backwards compatible with USB-A, but need an adaptor.
If you have a USB-C iPad then connecting to this port will provide faster syncing. It may also charge the iPad, though I’m not sure how well. Thunderbolt and USB-C ports typically supply more power than USB-A ports, but the maximum wattage supplied can still vary from device to device. I’d guess it will charge the iPad Pro (when not being used), but not as fast as the power supply that comes with it. Again, that is a guess. I haven’t looked into it.
The older 12.9 inch iPad Pros have Lightening ports, but are USB-C compatible. They should get the same advantages from the computer’s Thunderbolt port as the new modles, but only if you connect them with a USB-C to Lighting cable.
Older iPads can be connected to USB-C and Tunderbolt 3 with the right adaptor, but will only work at USB-A speeds. I’m not sure what the power limitaitons might be, but suspect they would be equivilant of a high powered USB-A port (5W?); capable of charging an iPad, but only when off and very slowly.
This is all off the top of my head, unverified. I’m open to correction on any and all of it.