Why is informal rule making often used by administrative agencies?

It is more efficient for the agency in terms of time and cost.

The informal rule making gives agencies the best and most unbiased data.

It is easier for the public to have a say in the rule$-$making process.

A public hearing is required, and this benefits the society as a whole.

A formal record is kept, which comes in handy for future rule$-$making endeavors of the same topic.