Researching a blueprint's ME (Material Efficiency) and PE/TE (Production Efficiency or Time Efficiency) to improve it can mean the difference between a profitable and unprofitable item. Instead of manufacturing everything myself which can require a lot of material, I've decided to research the ME and PE of some blueprints and then produce BPCs (Blue Print Copies) which can be sold to others for a limited run of production. BPCs are worthwhile because they have the same ME and PE as the original blueprint that you have been researching.
EVE is a game where you really see the necessity of specialization. You can't train all skills and you can't create and manage a whole production and supply chain yourself. I've learned this lesson the hard way which is why I'm only focusing on improving blueprints and selling them so that others can spend the time gather the materials to actually do the production runs.