A deep dive to 190 ft could technically be a no deco dive as it can be done within the NDL's (depending on what tanble you use) so depth is not really the defining criteria.
Generally a saftey stop is recommneded by some agencies on any dive below 60 ft. as it adds a margin of saftey. On any dive, rate of ascent is also critical and many divers have problems with maintaining a slow ascent rate of 30 fpm. A saftey stop helps as it gets the diver thinking about stopping before they get too shallow and can often prevent an inexpereicned diver form losing control of the ascent and gloing all the way to the suirface. The stop itself also reduces the risk of DCS due to higher than recommended ascent rates in additon to adding a saftey margin by providing more time to offgas.
But when you consider all that, it makes more sense to just address the fact that all dives are in fact decompression dives in that the ascent rate from any dive, short, long, deep or shallow, is an integral part of the deco profile. Some dives are just more deco than others and require staged deco stops as well.
Saftey stops are also just that - stops that increase the margin of saftey. So a diver regarding a saftey stop as being optional is about as smart as driver regarding good tread on their tires as being optional. You can skip them, but safety is reduced and just how smart is that?
