This expression literally translates as “Please keep your hard work!” or “Please do your laborious work!” At convenient store, for example, you’ve just bought a soda. You pay for it and say bye to a clerk; then you say, 수고하세요! It’s customary to say this expression to those who are at work; you are saying bye to them and leave them behind, and you know they keep on working there. At that time, this expression is the perfect one to say to those who are still at work.
This expression is the past form for 수고하세요. To those who did and completed certain work or job, you say this expression to recognize and acknowledge their work in a positive way. For instance, at the end of workshop, participants say 수고하셨습니다 one another and to the leader or to the facilitator.
Rather than its literal meaning, truly the courteous closing remark it is in Korean conversation! Thanks for reading this post, and 수고하셨습니다! *^^*