Aside from that they also have another purpose - to avoid compressor surge on light/low throttle.
Compressor surge = bad. As it is stopping the whole building of boost in the first place when on throttle as the BOV's leak at idle and light throttle.
Often people have noticed when changing to a 'hard pipe' kit, or taking the BOV's off and fitting larger turbos like 2530/-5s that they get comp surge uphill depending on throttle position.
So there is very much a purpose other than emissions/reliability.
Some users do have issues and have to return to the factory setup, some people dont. There are all sorts of factors from cams, piping choice & even exhaust flow etc.