It is correct, but (in my opinion) cannot be used too often.
It is a correct construction, but it has its unique purpose and therfore cannot be used in every situation.
A proper use would be in such situation:
Your colleague is always late for your meetings. The upcoming event is very important and you ddo not want the friend to be late. In this situation you can say:
"Please do come on time. It is very important."
By using the additional "do" you emphasize that you really want your friend to come on time in this case because it is more important than the previous times.
However this emphasise with "do" (as everything) cannot be overused. You do not need to emphasize every thing you say, but sometimes (as I showed) it can be useful.
So to summarize. It is correct to write such emphasized sentences with "do", but as everything it cannot be overused.