basically there are pros and cons to having a filter on your lens.
let me sum up the pros 1st:
1) filters are your 1st line of protection from any knocks, smudges, dust and dirts. meaning in case any thing happens, you just change your filter, not you lens. imagine spending a few thousand on a good lens then you land a scratch on it...?
2) there are also different filters to achieve certain effects you need. for example UV filter is mainly for protection, CPL filter is ensure light enters in 1 direction hence giving you a "bluer" sky and also prevent reflection. while a ND or GND filter gives you the extra stops you will need for you filter.
next on to the cons:
1) filters of normal quality some times degrades the image quality. however this is only visible when you pixel peep.
2) if you use filters on a UWA lens, it might show up on your picture...
so, if you do not know if you should get a filter or not, my suggestion to you is that you get a norm cheap filter on every of your lens. it''s for protective purposes more than any thing else...