If serves to get the job passed off for the inspection.if the red line of plumbing is necessary, what purpose does it serve?
Wet venting is allowed on bathroom sets, but not for laundry trays or washers.
If you are pulling a permit, and want to pass it the first time, you spend $3.00 more on pipe and get it done.
Otherwise, expect to spend friendly time with the inspector arguing about who knows more about plumbing. The inspector, or the homeowner.
I already know who wins that one
It doesn't matter which one wyes or tees off first, as long as it's properly vented when you do that. There are maybe four correct ways, and a bunch of wrong ways.
Venting breaks the siphon, which can pull the water seal from a p-trap.
When a washer pumps it's load out, that's a ton of water all at once.
When a laundry tray is suddenly drained, that's way more water than a lav drain.