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.
Here are two good YouTube videos showing better than I the advantages of having your own greenhouse.