Not a waste of time at all.

If my site was flooded with one of those fat belly adverts, no-one will click on it. By removing it allows other adverts to appear, and more likely to be clicked on.

If someone says otherwise, then they are pulling my kindling limb.

Martini Mate:

their Chrome AdSense toolbar now enables publishers...

Are they keywords? Dripping with the all consuming monster Google?

The full sentence reads

It’s a myth that filtering ads can prevent ‘low-paying ads’ from appearing, so as always, we recommend blocking only those ads that you feel are unsuitable for your users.

That is believeable. If you believe that "loose fat" ads or similar are not suited to your site then G is recommending that you block them.

For sure, those type of ads are generating income for G and by implication, for some webmasters.

I understand the full sentence to be saying something along the lines of in general G will place the highest (in their experience) paying ads on your site. Only block them if you believe they are not performing on your site.

I certainly don't block ads that pay pennies per click in the hope that they will be replaced by attractive ads that pay more. Off topic ads are another matter entirely.

Some years ago I was obsessive about my filtering ads and guessing which ones paid low and which paid high (I have extensive experience in AdWords which does give me a bit of extra knowledge as to some niches) as well as worrying over other aspects, and you know what, no matter what I did, the earnings were essentially the same. Maybe little rises, but nothing huge. So I have given it all up. The only time I'll block an ad now is if it's very obviously inappropriate for the site, or not working (I've had issues with a couple of rich media ads that just display as blank with nothing but the blue arrow)

This past year I pretty much enabled everything to run everywhere, and while my CTR is down, my EPC is more than double what it's been in any previous year.

The issues around my site, and placements and color - those are things I do worry about and obsess over, but Google does know more about serving ads than I do, and the less I try to tweak the dials, the more money I make and the less stress I have.

So yea, in my experience, it's a myth.

I never block an ad, and I believe blocking ads does nothing but cut your earnings.

If a belly-fat ad appears on your site and no one clicks it, Google's algo takes that into consideration next time it is in the auction. If no one is clicking the belly-fat ad, Google will stop displaying the ad, even if it has the highest bid.

By trying to guess which ads are bad for your site, and blocking them, you are reducing the number of ads competing for a spot on your site, thus driving down the winning bid and thus your earnings.

Google's algo knows a lot more about the user and ad performance than we do. In the long-run the best paying/clicked on ads will be displayed and you will make the most money.

I block the belly fat ads because I hate them. I don't care how much they might pay, I don't want them on my sites.

In one niche, I block advertisers who are in competition with a friend of mine. He never asked me to do that, but my own emotional logic compels it!

Well yea, those reasons make sense. I block ads just cause I don't like 'em too.

My site reviews new pop songs and our public is teenager users looking for new songs, but the top advertiser is a boring music school (not virtual). Do you think it's ok to block them in favor of people clicking more interesting ads?

Ads that you see are different from ads that your site visitors see. How often are you on teen popstar related sites versus how often your site visitors are? How often are your site visitors on a youth clothing site versus how often you are?

It is very likely that the ads being shown to your site visitors are different than what you are seeing because they visit different sites and because of that are shown different ads based on the sites you and they are visiting. Geographic location also influences the ads your site visitors see.

You can go ahead and block the ads that you find irrelevant, but the advertising experience you are changing may be limited to your own, not to those who are visiting your site.