Some channels are just really egregious about the quality and quantity of their sponsorship ads. For example, the podcast Talkville, a podcast for the show Smallville, has overlong intelligence-insulting ad reads. Sometimes the ads are edited in to cut off whoever was talking mid-sentence and the show doesn't resume on what was cut off. The ratio of ads to content is also quite bad. If you contrast this with a podcast like Trash Taste, they have short, snappy blurbs about the product that attempt to be entertaining and get you back to the podcast asap. The time spent on them in total is much lower despite their episodes having double the runtime.
I have since stopped watching that lousy Talkville podcast, but I just wanted to illustrate that why you might want to block sponsors for certain channels