A lot of the Indian riders seem to think the engine guards are there to keep their legs from getting trapped under the bike if they get in an accident.
There are also a lot of Indian riders who claim the RE engine guards will trap their legs when the bike gets in an accident. This is especially true with their thoughts about the guard that is styled to wrap around the area where the riders feet are.
Personally, I wouldn't rely on them to protect or trap my legs in an accident but they are useful for giving the motorcycle some protection as it goes sliding down the road after an accident.
During my 12 years of riding my BMW, its engine guard bars probably saved me at least $1000 by protecting the expensive valve cover. (It was a 3 cylinder K-75 with its DOHC sticking out the left side).
So far (with the Honda, Suzuki and BMW) every time my bike has hit the ground when I was riding it, my feet were well above anyplace that could be trapped by engine bars because I've always kicked up and off as the bike was going down. I usually ended up either sliding along side of it or riding it like a belly board.
Personally I like them if the bike is set up as a mild "dresser" and I think they are absolutely needed to make a Military bike look the part.
I wouldn't put them on a scrambler or cafe racer though. To me, they would look totally out of place on either of those.