As total concentration is needed while shaving, after a few cases of ears lips and noses being sliced due to early morning and late night shaving while being tired it was decided by the bods in shaving manufacture to incorporate an early warning system of some kind, the boffs not wanting to radically change the head of Razors decided to shorten the edges of the head giving that overhang as an early warning system to waken us from our slumber so as only to cause a minor scrape without amputation or upsetting our Loved ones nice clean Bathroom by spilling copious amounts of claret where the possibility then lay in physical retribution from her/him (insert as appropriate) & it being rather more painful and possibly maiming us to boot.Never really considered the reasons for this. (shows my attention to detail)
Having said that when using razors which don't allow overhang I did find removing the blade that bit more difficult, particularly when it decides to stick to the top cap.
Despite this I see that razors without overhang are favoured over the ones which do.
For example Tatara's latest addition the Muramasa no longer has the overhang.