Looking to build desktop PC to use with monitor which has Thunderbolt 3
What does a Z390 (with Thunderbolt 3) give me over a Z370 motherboard?
No other T3 peripherals at this time but I am looking to future-proof (as far as is practical)
Connecting your monitor with TB3 would mean you're running it off of integrated graphics. There isn't really any advantage to it except it allows you to use your monitor as a display + hub (assuming it has additional USB connectors) with a single cable.
Ok, that's fine. I still don't really see any advantage to using TB3, given that you'd be paying a premium to either buy a TB3 adapter or get a mobo with one included. Do you already have a TB3 display?