I think it defiantly depends on the situation. I haven't run into creators telling me this, but as a creator I did run into a situation where I had to tell readers this.
The only time I have used this is when a group of gun enthusiasts started harassing me about how they couldn't tell the exact models of handguns I was using for my characters and that it was 'problematic' When I explained that I'm not actually trying to draw any specific models, I'm just going with the general shape / silhouette of the type (like you can at least tell that they are a handgun / revolver or a sniper for example) for artistic reasons (and sanity because I'll have to draw those things hundreds of times in a comic, if they get too details it's gonna drive me nuts) they got extremely pissed off at me and REALLY tried to push and harass me into drawing exact models of hand guns because it's insulting and problematic and disrespectful to gun enthusiasts who want to be able to tell exactly the make and model of the guns their fav characters are using.
So I gave them my reasoning and they would shoot it down, saying they're 'just excuses and not good enough reasons' (artistic rendition / I need to draw these thing repetitively and I just can't / It would take to long to do that kind of detail and don't get paid enough for that as at the time I got paid for release speed, not detail / it'll look REALLY out of place in the art-style to name a few) so in the end I told them something along the lines of "It's just a comic." as well as "How come you're questioning me on how unrealistic it is for me to not draw the guns as exact realistic models but you're not questioning me on how unrealistic it is for everyone to be an animal person? (it was an anthro comic)"
It wasn't meant as a insult, but more of a 'what you're requesting is unreasonable' especially when I got paid as little as I do to make this comic. My situation / contract / health / creation and design process just wouldn't work for it, but any other reason I brought up was fought with with reasons that just didn't overwrite those problems despite them thinking that it did. So in the end that's all I felt that I could say about it.
Honestly, the person I hear this phrase from the most is myself, because I have a bad habit of overworking myself to the point where it physically damages me, so I need to reminds myself that 'it's just a comic.' to remind myself that my work is not more important than my health.