There are always pro's & con's when modifying your rig & adding a "tactical" or oversized bolt knob is no different. Here's how I see it:
Does assist with bolt manipulation as it usually makes the lever longer.
Easier to "find' as you're observing through the scope
Some of them stick WAY out there, making it possible to snag on things you don't want it to.
Can be a real PITA when you carry the rifle slung over your shoulder, the knob can dig into your back/side.
If you're looking for an easy route, I was able to install one of these myself:
TACTICAL BOLT KNOB CONVERSION - Brownells