When planting seeds inside it gets sheltered bonus: decrease growth time, compared to outside: increase growth time. When it rains, outside also gets the soggy debuff: increase growth time.
Yet planting seeds outside in the rain will grow way faster than stuff inside. I used the same seeds inside and outside, and even though I planted and watered seeds inside first, the seeds outside were grown about double as fast.
Adding on to this with a screenshot. This was taken from a plant box I had outside. As you can see, there are red down arrows saying "increases growth time" and green up arrows with the same wording!
Will the real benefit and detriment please stand up and introduce themself/-ves to the group? :)