HF, I always try give you 170kts (or at least up to 6dme), the lack of requests for 170 to 5 make me wonder if I'm doing the right thing!
Is it beneficial for all 737s at all weights?
Pretty much all of the time, it is beneficial. We don't ask because we rarely get (or is that just my experience?). The only exception is for a weight above 53 tonnes where we have to increase all minimum speeds by 10kts. (ie. at 53.1 tonnes and Flap 10, 180kts is as slow as we can go with the gear up!!). Max landing weight for the -300 and -500 is below this therefore it is not an issue. The exception is the -400 which has a MLW of 54.8 tonnes. However, it is unlikely to be this heavy on landing unless tankering fuel, which we don't tend to do into LGW (oops, gave it away!!) so this situation is practically never encountered there.