As long as we're following the FCC rules, there's no other rules to follow when using FT8 or any other WSJT mode. I see things like sending grids and the final 73 as optional. By stations sending their grids on 6M & 2M, that makes it much easier for grid chasers to spot needed grids. This is especially true when the bands are open, and calls are rapidly flowing in. I see no need for grids on HF. Seems like there was a grid chase going on, or maybe still is on HF, but I only chase grids on VHF. JT Alert won't catch needed grids unless the callers are sending them. So I end up having to pull stations up to see what their grids are before deciding to work them or not. As for that final 73, don't see any need for it, but send it anyway because there's some who won't log you without it.
HamQTH makes looking up a station's grid faster, because the grid is on the first page. With QRZ, you gotta switch to the Detail page to see the grid. And for freeloaders like myself, you won't go past your allowed number of look ups on the Zed if you're using HamQTH.