I know people have stated their points here but it's BAD to run without a BOV period. Doesn't matter if you're running .2 bar or 2.2 bar boost, it's bad and will damage your turbos. Even if your wastegate is set at 5psi, when the TB closes and that pressure has nowhere to go it will rise, as everyone knows. However it will continue to rise WELL in excess of 40-60 psi between your compressor wheel and the TB in a blink of an eye. To backspool and stall a compressor wheel that is spinning at 60-120 thousand rpm under full boost takes a massive amount of boost pressure and that's exactly what happens when your BOV jambs closed or is block off
Try this sometime.....ok maybe not but at least vision it
Block your BOV inlet off and hook a cheap boost gauge to your charge piping or IC and watch it rise after a hard acceleration. 90% of aftermarket turbos are NOT designed to support that type of pressure differential and fail.
Compressor surge damages turbos VERY quickly, especially floating bearing types as it wedges the turbine shaft against the side of the bearings. Remember, floating bearing turbine shafts DON'T actually touch the bearings in the CHRA but rather float on a film of oil at about 15psi of pressure. I've replaced turbochargers that failed from C.S. where compressor buckets(the blades)have folded back or broken right off and even times where the turbine shaft has snapped right clean off right behind the compressor wheel(thrust bearing)
Being a Garrett dealer I'm always advising my customer during a turbo R&R to thoroughly clean all oil lines and passages to and from the CHRA, as well as check the operation of their BOV. Your engines are not diesels and thus need a BOV to maintain turbo life(diesels have no TB's thus no compressor surge). Recirculatory style valves offer no more "spool reduction" than atmospheric styles. They just vent boost air back into the intake tract that has already been used to calculate fuel input, weather it be by a hotwire MAS or a CIS flapper valve. It's dumped back into the intake tract to prevent an overly rich situtation as you let off the gas during shift or coming to a stop. Old DSM's have a problem with people venting bov's to the atmosphere and the stumble/stall due to this phenomenon. Atmospheric BOV's, by manufacture's design, tend to flow more air than recirculatory types and thus are used more often in high perfomance upgrades. Or as stated, multiple BOV's are used to vent enough air fast enough. When you've got twin 90mm compressor wheels forcing 30+lbs of boost into a motor, that can equal quite a bit of compressor surge if a valve went off the deep end
Sorry for the long post guys. I go off on a tangent with these things sometimes. Just trying to keep your turbos alive