Saving our own seed for sowing over the following years is probably done by most of us for economy, convenience or security. I guess most of us save seed for the latter, for security; of favourite varieties, in case we may not be able to replace them otherwise. If you have heirloom, expensive or rare varieties then saving seed is a real necessity. It is obviously little effort to save back a portion of seeds of those crops grown for their seeds, such as peas, especially if these are large heavy seeds expensive to buy.