Only problem I see really with a ton of junk food, would be it doesn't fill me up as much, so I eat in excess when I put the junk food in my system. Feel like healthier foods also tend to give me more energy
The nagitive effects are probbly more long term. Most of us only have time for 30 mins -2 hours a day of gym time, and not allways 5-7 days a week. Thous making it harder to work off what ever short term negitive effects. If you're a profesonial athlete able to devote 4-8 hours a day 5 or 6 days a week. Junk food won't effect you as much in terms to size and porformance.
^ If you moderate your 'junk food', then it's not going to have any long-term damaging effects. If you're trying to justify eating nothing but **** by saying "Well, it fits my macros bro, YOLO", then yes, I agree. I think a lot of the time when people talk how junk food makes them feel crap it's more psychosomatic in all honesty.
Let's say you eat junk food once a week and eat healthy for the rest of it. I don't think it would make a serious diffrence.