Depends on the lens. The deep lenshood protects most of the bigger telephotos. In 20 odd years carrying a 400 f5.6AIS Nikkor, never had a problem and this survived some rough country. The body was worn and chipped, however. Many of the exotic primes are designed with a flat protective element, which, apparently, is 'relatively' cheaper to repair (!)
Some smaller lenses, such as 58 f1.4G Nikkor have a deeply recessed front element, as do the 55 and 60 Micro-Nikkors. Why use a filter with these optics on a digital camera, unless a CPL?
There's a different risk category for primes with large vulnerable front element (eg 85 f1.4AFD and many UWides). If not using a CPL, I keep a protect filter on, mainly as first point of impact (potential one always hopes). I standardized on Marumi Fit+Slim MD Lens Protect. Also keep one of these on the 300 PF, as its flimsy hood is the only weakness of this superb little lens.