As a general rule-of-thumb strange/wonky proportions are usually alright in some cartooning styles as long as it's consistent. For instance, if a character has a weirdly skinny body, then they'll have a weirdly skinny body all throughout the work. Wonky body proportions is all about inventing your own rules and sticking to them. The biggest challenge with this, however, is that the new rules are usually based off of realistic anatomy rules (e.g. the annoying proverb of having the learn the rules to break them). It's always beneficial to learn/understand real anatomy better, regardless if you want to apply the rules directly to the wonky style or not.
Regarding actual off-modelness, this is my opinion: a little difference here or there is okay for sure, but if it's noticeable enough to make seasoned readers unsure of who someone is, it's probably a problem. On the other hand, if the readers can read through a comic and still recognize the characters and understand the plot despite a bit of off-modelness, I still think the comic could be considered successful. If the off-modelness is confusing readers, interfering with the reader's ability to read the comic (e.g. all they can see is that huge nose rather than the punch-line in the corner) and otherwise causing unnecessary problems that could be fixed with better proportions, however, I think it's something worth changing.
Personally, my biggest problem with off-modelness is keeping character's clothing consistent. I keep on forgetting if someone's wearing laced boots vs. non-laced boots, if a vest has a collar, or if someone's shirt is tied off at the waist or not. Sometimes when I'm inking I see pencils where someone's jacket just completely vanishes! Body proportions I'm not usually that bad about, though sometimes I draw character's faces pretty badly and have to edit them later using Photoshop.