Why is estimating important when dividing with decimals?

Answer 1

Using an estimate ensures that the answer is about right. With decimals where the decimal point should go is difficult for a lot of people, so an estimate of the answer ensures that it is put in the right place.

Answer 2

It is not important for all. However, many people find it difficult to judge where the decimal point shuold go in the quotient and for them having an estimate can be useful.