The negative impact is, There is a lot of litter, alot of noise and alot of drunkness... Greece is the most visited area and has the 2nd largest crime rate.. 3/5 People in Greece have been arrested...
If it is tourism in the United States that includes purchases then it is beneficial to the economy, but if it is another country or it doesn't cost anything then it is a good memory with whoever you...
In a nutshell, employment and money. Tourists need places to stay, eat and shop. That creates jobs in hotels, restaurants and stores and gives those businesses money that they can then spend locally...