"When in Rome,do as the Romans do" means that when you are visiting a new place,you should try to do as the people do who are from the place.
People from different places have different ways of acting,so it is important to try to do things the way local people do.Because this will make the local people feel more comfortable with you around,also you will feel closer to their culture.
So,imitating the local ways,you will learn more about their culture and tradition,also,you will be able to make many new friends.:)
Also,it could be fun.The traditions of the place you are visiting might be different and interesting at the same time.If you "do as the romans do",you will do a lot of things that you wouldn't normally do.Who knows?Maybe you will discover some new talents in you.
Therefore,I think "when in Rome,do as the Romans do" is a very good advice to tourists and visitors.
很短...^.^