I'm quoting Marek's answer from the question : Difference between electric field E and electric displacement field D
..materials have lots of internal charges you usually don't care about. You can get rid of them by introducing polarization P (which is the material's response to the applied E field). Then you can subtract the effect of internal charges and you'll obtain equations just for free charges
I couldn't figure out what are the exact effects he is talking about at first. After that I saw that maybe it is due to the fact that bound charges do not contribute to electric flux desnity field D outside the material (because flux line originates from bounded positive charge and terminates on bounded negative charge inside the dielectric, is it correct?). Is it one of the reasons that we are at large not interested in bound charges and have developed suitable mathematical ways to eliminate troubles caused by them? Are there any other reasons?
Thanks in advance.