If you've got 40-50mm of lens hood on the end of 120-150mm of lens, some people will be more prone to bumping their camera into stuff with the lens hood on, rather than off.
Like I said, coated lenses rarely have trouble with stray light (how many pictures have you seen, even snapped by people using film or digi point & shoots, that have lens flare evident? I haven't seen any, except from so-called "lomographers").
Also, lack of a lens hood doesn't leave the lens exposed to dirt. Lack of a "sacrificial" filter might leave the lens surface prone to dirt,, but a lens hood is only there for one reason - to cut stray light in the tiny minority of shooting situations where you might need it.