Protection

• A lens should always be protected from dust and scratches. The lens cap can be used for this purpose; however, if the lens is exposed for long periods of use, a filter may be the only practical way to protect the glass.
  
  

UV Filter

• A UV filter is the most common type of protective filter. It filters ultra-violet light which may enhance distance shots.
  
  

Multi-Coated Filters

• Multi-coated filters resist and minimize the appearance of scratches.
  
  

Breakage

• In the event that a filter breaks, it may also damage the lens. However, generally an event that would damage the filter would damage the lens anyway.
  
  

Distortion

• Filters do provide a very small amount of distortion. But for most photographers, this is unnoticeable.