I grow veg in southern England, starting from seed in a south-east-facing windowsill. I already use a heated propagator for my seeds as my house isn't very warm in early spring.
The garden has mature oak trees and a hedgerow along the south east edge, so by mid summer is fairly shady, though most gets some full sun each sunny day. The other side of the hedge is fields, as we're on the edge of a village.
The same trees, even when bare, partially shade my windowsill, and everything seems to get off to a very slow start.
Thinking particularly of tomatoes, chillies, and aubergines, my annual veg, whether grown outdoors, in a lean-to greenhouse, or kept in the kitchen, is several weeks behind a garden about 300 metres away. That gets more sun, and being a couple of streets into the village may be a little warmer. Neither of us is a heavy user of fertilisers. Even the wild blackberries in my hedge are behind those nearby.
I can give the hedge and the lower branches of the oaks a little trim, but even if I wanted to, couldn't make major changes - they're not mine, and they're protected. I also like having the shade on the house when the weather gets hot.
I'm considering grow lights to accelerate my seedlings next year. Will the boost early in the season be maintained later into the year, or is it not worthwhile?