I found that exercise helpful, because I could see what it was doing to my writing style. This also meant that I knew when that "rule" could be defenestrated. Doing away with those verb forms (and adjectives or adverbs) does make a scene more vivid, but sometimes a vague or telling scene is more appropriate, or your style could be vivid enough that a reader will stay with you and your to be verbs, adjectives, and adverbs.
Chuck Palahniuk wrote an essay about doing away with "thought" verbs, because it means that nothing is happening. It's worth checking out, here:
http://litreactor.com/essays/chuck-palahniuk/nuts-and-bolts-%E2%80%9Cthought%E2%80%9D-verbsI'd like to contrast that with Gail Carson Levine's essay in her book
Writing Magic, where she demonstrated with excerpts from her own books that "show, don't tell" is too proscriptive.
"Show, don't tell" is a good rule for television and films, visual media. That, I believe, has influenced writing conventions. Writing conventions are just that, conventions--and they can be bent or broken. (As an aside, one of my favorite shows right now have all of the characters speaking in exposition for most of an episode. The actors are so excellent that I don't usually mind.)
If you don't even really know why those conventions or suggestions exist, or your mentor who's making you write like that can't explain why they're suggesting it, then I certainly wouldn't recommend following them.