The citrus that is typically grown for fruit has been grafted onto less-edible but hardy rootstock (sour orange, etc.). Planting a seed will produce a tree but that plant may be more susceptible to cold and disease damage than grafted plants. Additionally, the juvenile period (when stems are thorny) can last several years before reaching the reproductive stage. If that isn't enough, you can not predict the quality of fruit because it is genetically different (product of sexual reproduction). Glass half full: You may actually get something better than the parent. Glass half empty: Many times its is something less. Here's to a full glass!