This is an area with so many options it can get confusing as to what you really need. My rule of thumb is to protect things that are either very expensive to replace or will leave you stranded in this first round of protection items.
If you are planning on any sort of off-road riding, even just some gravel forest roads, you’ll want to make sure you have underside of your engine protected. I don’t think I need to go into too much detail on the repair costs caused by a cracked engine case or ripped out oil drain plug. I can’t think of any motorcycle that leaves the factory with a robust skidplate. At best there is some sort of token piece of metal bolted under the engine, but more often it is flimsy plastic, or in some cases nothing at all.
Engine Crash Bars
Like with the above, this is all about protecting the engine, the heart of the motorcycle. On BMWs with a boxer engine these will protect the cylinders. The usefulness of engine crashbars isn’t limited to off-road use, even a parking lot tip-over will prove their worth.
Damage to the headlight can limit you to daylight hours only. Beyond that fact, many of the motorcycle manufacturers have stopped offering replacement headlight lenses. This means if you crack the lens you get to spent hundreds of dollars to replace the complete assembly. In the case of the liquid-cooled BMW R1200GS, the LED headlight assembly retails is the ballpark of $1,200.
Choosing between a clear plastic or metal mesh style normally boils down to rider preference. A clear plastic headlight guard will provide complete coverage, but as it gets dirty the headlight’s effectiveness will decrease. On some applications a dirty, clear headlight guard will also deflect light back at the rider causing glare. With the metal style you’ll notice some shadows from the guards at the far edges of the headlight beam. Personally, I use the metal style, but chose for yourself, they both have advantages.