Is it necessary to have such temperature precision: 19.8 degrees or
 17.3? Personally I usually look at the weather estimates and try to
 round to the nearest multiple of 5. Say, if the estimate is 17
 degrees, then I will try to remember 15 degrees. If the estimate is
 18, I will think of it as a 20 degree estimate. So in this sense, is
 the decimal precision really useful? Wouldn't it be better to round
 19.8 to 20 and 17.3 to 17? 

The same doesn't hold for speed estimates, where decimal precision looks nice.