I've enjoyed having a little greenhouse this past year. It's made a great difference in my gardening. For one, it extends my growing season considerably. Also, I successfully started many plants from seed. I've been particularly happy with my petunias. I collected seed pods from last year's petunias and have had great success. They don't necessarily breed true to original color, but I enjoy seeing what nature comes up with. I've also had success with tomatoes. Never before have I had much success at all growing anything from seed.
I was recently gifted the big tent like greenhouse you see in the photo above. You can see the comparison in size and shape with the smaller greenhouse next to it. I have both. The smaller is easier to assemble but the large one has much more space to move around as well as windows for ventilation.
A variety of pink petunias I grew from seed in my greenhouse this spring.
Here are two good YouTube videos showing better than I the advantages of having your own greenhouse.