Let's just say a person is an idependent contractor say in IT.
How would that person have any idea whether or not they will have work in future quarters? Again it is not really quarterly installments.
The other thing an idependent contractor has to deal with comes down to timing issues.
Lets just say they are owed money and they do not get the check prior to 12/31/??
The check may or not be mailed but actually dated in a different year. The check may be sitting printed in a drawer but not mailed. The person doesn't have the money but it is included in a 1099 for that year.