More affordable flight tickets and people in need of the sun (or snow) causes many destinations to get flooded by tourists. Many European destinations depend on tourism for income generation, however these destinations also feel the negative sides of mass tourism. Places like beaches or restaurant areas get overcrowded, causing many local people to leave to other places. Tourists can create too much noise for locals, causing, for instance in Venice, Italy, the creation of new laws regarding bringing suitcases with wheels (hard wheels are not allowed anymore as they make too much noise on the streets).
Mass tourism also brings a big problem of pollution with it. People bring their own snacks and leave the packing behind on the beach or in the nature, which disturbs and kills (marine) life. Bali is one of the mass tourism destinations dealing with a huge waste problem, mainly caused by mass tourism. For all these reasons (and many more) I would like to advise you to choose a destination that is not flooded by tourism, a destination that can handle the amount of tourists coming to the area.
However, I also want to stress the fact that lesser known, deserted places are also not always the best decision. A place that is not at all ready for tourism, can be damaged very easily and the local community and environment can get harmed by tourists, when not dealt with properly. So think about your next destination and how you as a tourists could positively and negatively influence the place.