Many gardeners begin their vegetable growing experience by sowing and growing outdoors.
It doesn't take too long before the realization dawns that sowing indoors and getting seedlings off to a good start before planting outside is a good idea. Of course this may not be suitable for all vegetables, but it is a good thing to do for tomatoes and other subtropical plants like sweet peppers that need a bit of extra TLC to germinate and get established successfully.
One of the greatest benefits is that a greenhouse extends the growing season making it possible to start plants early and protect them when the weather turns cold, towards the end of the season.
Further protection from the rain, wind and cold temperatures, especially at night, makes the greenhouse indispensable but there are few negative points such as it may be more difficult to control aphids and high summer temperatures. However, good aeration and shading from direct sunlight can help relieve both problems.