I block ads because of three main reasons:
1. I don't like being tracked by a third party
2. I don't like visually annoying ads (blinking, moving, changing, etc) - I can't read a page if it feels like I'm in Shinjuku or Las Vegas.
3. Ads are often destructive, either they popup (in the page, or in a new window/tab) or they contain trojans or worms
Since I block lots of trackers, already there most ads vanish. Domains that serve any of the catagery 2 or 3 are also blocked - actually all third parties are blocked if they are not needed for the page. (RequestPolicy. It's a bit of work and why the can't people make pages without dozens of third parties anymore?)
Pages that don't have third party ads are not blocked in any way.
Pro tip if you want your ads to be viewed:
1. serve them on the same domain
2. don't animate them (maybe don't even use images)
3. don't make them have any sort of script
I for instance see google ad-words. I just can't click on them because it leads to a blocked tracker domain... :p