From looking over your posts here it’s hard to see where you are at in your progression. I would guess that you know a vest makes it harder. Maybe if you are doing the majority of the WODs as Rx’d, and your times are approaching an “elite” level this may make sense. You could also just up the loads (like heave Fran etc).
Often times people do workouts with a weighted vest on but usually it’s not within the intent of a metabolic workout to have one as a regular occurrence. Workouts that are meant to be a metcon will not usually maintain that element with added weight, however doing so once in a while is an interesting variation.
However, if your metcon workout times are in the range of the likes of Chris Spealer and Jason Khalipa then adding a vest to “scale up” isn’t uncalled for.
Some workouts that are often performed with a vest are “Murph” (rx’d calls for 20# vest), “Cindy” and sometimes even “Fran.”
Frankly, the vest just adds a level of suck. It can mess up the point of a wod if you’re not careful. That’s not to say you can’t use one once in a while, but most of the time it slows you down without a lot of good to show for it. I’d almost go so far as to say that the wods need to be designed with the vest in mind and that doesn’t happen very often.
Often when I strap on my vest it is because I’m dragging and don’t want the sprint of a raw workout. The individual reps are harder but the overall WOD doesn’t get me red lined like a body weight only workout does. They have a place but I’d avoid using them in sprint type workouts as they will totally blunt the intended hit.