It applies to beers where the esters the yeast produced are wanted as part of the flavor profile. Things like wheat beers and Belgians wouldn't taste the same without these esters.
For other styles you usually want to keep these in check since they are not usually wanted in the finished product.
Ideal temp for ales is in the 64-72 range, although some ale yeasts ferment well down to 57 and some up to 80 degrees. A Bavarian wheat should have some banana so low to mid 70's is fine. Just check the ideal temp range for your particular yeast to see where you should be.