Wasted material is wasted money. Over the years I have tried to analyze the remaining impression material or bite registration in cartridges and make the decision whether there is enough remaining material to accomplish our goals. If not time to use a whole new cartridge. We have also loaded two separate guns and used the remaining material, switched guns to finish loading the impression tray or taking the bite. This approach uses two tips, another way to increase costs.
Recently we became acquainted with a product called Lock-n-Reload. The blue plastic connectors fit on to the end of the cartridge of material, and allow you to attach a second cartridge of material. Using the gun you move the remaining material from cartridge one into the second combining the contents. The now empty cartridge and connector are thrown away and you can get full use out of the material. The connectors are manufactured by a company called IndiGreen Innovations at www.IndiGreen.com and is available from most of the major dental distributors.
Wax used properly is probably the cheapest and accurate bite registration out there.