It is helpful for your health. but there is no absolute guarantee, you still need to do many things else to prevent sickness, e.g. healthy diet, proper exercises, enough rest and sleeping, regular daily routines.
Washing your hands several times a day also helps prevent illness. Not excessively, but when you have been using someone else's phone or keyboard/mouse, or shaking hands a lot. Whatever other people touch a lot, or that many people touch, can carry lots of germs from all the times they touched other things. And lots of people don't wash their hands after using a bathroom. Imagine touching something that 20 other people touched, and 10 of them don't wash their hands after... Just keep lotion handy for dry hands.