Well, there's a lot of factors that go into light leaks being bad. As always it's not that simple. Indoors, a light leak can be a horrible thing. Inside plants are coddled and haven't build up strength like outdoor plants have. Outdoor plants face greater temperature fluctuations, light exposure of leaks from the beginning of their life to the end, and the outdoor girls get strengthened by winds.
It's also a matter of lifelong exposure to the light "leaks" that they face. An outdoor plant is exposed to this from the beginning. It spent it's whole life exposed to the moon, street lamp, stars, ect, so it's used to it and it's a part of it's routine. An indoor plant has a very specific light schedule and if you suddenly interrupt that with a leak at some point in it's life it will throw it off.
I have also had street lamps fuck with my outdoor plants. Last year my asshole drunk neighbor a few houses down decided to put in a flood light and leave it on all night. This is fine in a rural setting but a huge fuck you in a city. The light caused a significant delay in flowering for my backyard girls and as a result they went way longer than they should have and drug on into mold season. I also ended up with a few seeds in my buds somehow, most likely that fucking light. That isn't the first year that a light has fucked up my plants either.
So yeah, circumstance depending a light leak can be a real pain in the ass. That's why all the best growers and pro setups are light sealed, it's not a gimmick or a scape goat.
