Depends dude. If you're a big fan of bf3/bc2 then I would recommend leaving it off so you get that zoom when in ads. From what I've gathered if you want the same zoom level for irons in bf1 as you didn in bf3 with rds/kobra then set sights to 2.00x zoom, turn on ads field of view, and then set your fov to 72. Should be pretty much identical when in ads in terms of zoom for iron sights. However you're gnna have to change your sensitivity for zoom to half your ads hipfire to get the same exact feel as bf3. Sorry if you've never even played bf3. Was just using that as my reference point as it was my main fps games for ages.
If you're a big fan of csgo however then i'd say keep the irons at 1.00x zoom and turn on ads fov option to get no zoom as it will feel more natural. Also make sure
that uniform aiming option is on to get a 1:1 ads hipfire sensitivity to mimic csgo.