A couple of years ago I got involved in a big project involving handwashing. There are 2 types of bacteria on your skin - 'resident' and 'transient'. Resident bacteria have evolved to live on your skin and are, essentially, part of you and transients are those that you pick up from external sources. Resident bacteria are usually benign (unless your immune system is compromised - when some of them can turn nasty) and some transients can make you very ill or kill you.
Luckily, although residents can be hard to dislodge (because they have evolved to stick to their host - ie. you), transients are fairly easy to wash off; this is why you need to wash your hands.

It would appear that every part of the body (hands, feet, scalp, armpits, groin etc.) has a different resident microflora and these different floras may play a role in maintaining skin health in those areas. I say 'may' because after reading dozens of scientific papers in this area I never came across one which declared definitively that this was so. Nevertheless, there appears to be a suspicion that killing everything on your skin, with aggressive anti-microbials, may not be good for long term skin health.