erm, sorry, little lost on this one?
Changing a pollen filter, I think, is part of the service schedule on most cars? Ie, if you have a look at ur manual/service log book etc I'm sure you'll probably see when it should be changed. I'd guesstimate at every 20/30k?
Advantages? Well, other than a cleaner filter and hence less pollen and sh*te from the outside world, nothing?!?