In the summer I use an additive that cleans the injectors..
In the winter the fuel changes, so I add Hawes Diesel Treat or Kleen Flo to compensate for the reduction in the sulphur content in the fuel. These additives assist in lubricating the IP. Winter fuel is formulated differently to aid in cold weather starting, and some lubricants are reduced to enhance volatility, as has been explained to me.
Here in BC we have provincial government mandatory "Air Care" testing of all vehicles (California North!) and they test opacity in diesels. My 250000 mile 300D emitted only 40% of the amount of opacity that is deemed to be the maximum allowable. I have not replaced injectors or glow plugs in several years. I attribute the general smokelessness and good emission test results to my regular use of additives, and almost daily fast highway driving.