Are there only advantages or also disadvantages of speaking a language that everybody understands?

This is a question meant for the people with English/American as their mother tongue. What are the advantages and disadvantages? Do you speak any other laguage?
Update: What I mean is: almost everybody around the world understands English. I personally have Danish as my mother tongue and speak English as a second language. When I speak my mother tongue, only a fraction of the world's population understand me. I think there are both advantages and disadvantages of that - but... show more What I mean is: almost everybody around the world understands English. I personally have Danish as my mother tongue and speak English as a second language. When I speak my mother tongue, only a fraction of the world's population understand me. I think there are both advantages and disadvantages of that - but I'll always be understood in English. I just wondered if you see any disadvantages of speaking English - especially if you don't speak another language. Hope, I make more sense now.
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