Am I never going to get the best out of a field by using them?
In a word, no. Whilst I will always add shot birds to the pattern, I have never started a day out pigeon shooting solely with dead birds.
Artificials are so much more convenient and easily stored and transported.
Also, pigeons saved from a previous trip never look quite as bright and fresh as birds shot on the day, quite apart from the fact that I often start the day with 50-60 plastics, a number that would weigh 60- 70lbs were they dead birds.