It is as Jura said. Both expressions mean the exact same thing in that you would be asking someone to continue speaking, whether they were interrupted by someone else ( for example, someone poking their head in to give a message or ask a question during a business meeting) or the speaker stopped (for example out of concern that there was no longer time to finish). In either case you could use informal expressions such as "go on" or "carry on" or a more formal, polite term such as "please continue". In a formal setting such as a business meeting it would be much more appropriate to say "please, continue" rather than "go on" or "carry on" which you would use informally with friends and family.