Most bicycle accidents without helmet lead to skull damages.
Most bicycle accidents with usual bike helmet avoid about 30% of the skull damages. (c.f. Swedish STRADA accident database).

No data on full-face bicycle riders is available since numbers are too low to reach to any statistically relevant conclusion.

It seems obvious, that full face helmet will reduce the skull damages caused when
the traditional bicycle helmet is pressed backwards.
It also seems reasonable that full face helmets will help avoiding mandibular damage (symphysis or tooth loss).
Risks on additional risk for spine damage has been reported since full face helmets weigh more than traditional bike helmets. Nevertheless, bicycle crash speeds are
comparatively low so this might not be even a measurable effect.

I commute 50km a day (round trip) and I always use a Bell Drop full face helmet. Before that I had a Bellistic.

Vision is not reduced too much, with a full face helmet, you will learn to turn around your head a bit more than you are used to. A potentially healty side effect is,
that car drivers realizing to be watched at tend to behave more careful.

Bell helmets are very well ventilated, they do not get too hot (outside temp up to 28C), nevertheless, the advantages are great in winter time. No need for
balaclava towers and other constructions - simply switch to a motorbike helmet when temperature is below -5C.

Using to do downhill, I simply put on my downhill gear at home before biking to the hills. Then I used the stuff for commuting and felt terribly
watched during the first weeks. Nevertheless, things settled down after a while and now i feel unprotected without the stuff.

So my recommendation: Simply use a full face helmet whenever you feel for it.