I have a relative very low understanding of deco but It strikes me that the deep stop rule of half ATM is just another global rule of thumb. The words unneccessary and increase deco overall is very dependant on IMO what you have done so far. By that I mean doing a 100 ft dive to the ndl limit vs doing a 100 ft dive as a bounce to get a dropped tool etc. Time has to have a lot to do with just how much continued on gassing you would be capable doing let alone anything else. Yes I think a 60 ft dive for 20 min and a "deep" stop at 1/2 ATA is a waste. but a dive to 130 for 5 minutes and stopping at 50 ft is a whole different thing. IMO especially when you look at the aspect of potential harmful continued on gassing. Again from a pure novice perspective. The idea of any rec stop deeper than 15 ft is not a good idea is questionable. That too is riddled with IMO problems as rules like,,,,, do a 3 minute stop at 20 is a global one based on the worst condition dive. If you take the argument of rec diving is to 130 ft on dive tables and you start to ascend 10 seconds prior to NDL I dont think 40 or 20 should be a no no or a waste. but if you use the RECOMMENDED max depth for an OW of 60 ft on a computer it is again another story. Personally I have always believed that deep stops are a TECH THING and use it for a deep stop and combine other activities inthat period. That many rec divers follow suit for the 100 ft plus rec dives for when they screw up their ascent rates or run at min consrervitism. I can also see that opinion of physics if you are a skilled master at ascents and not having to do some stops. but the real world is not like that. You can beet feet to 60 and slow your ascent to 30 depending on what era you certed in . the 60 fpm or the 30 fpm or the mix. Thankfully the GF displays on my shearwater take the mistery out of what to do when that question of stop or dont stop arrises. stop depth for safety or other ,,, gf99 tells me that min depth limt.,,,,,,,,,,, how long to stay???. gf surface tells me that min time.