Why cakephp fire exists() query before inserting/updating data


I am using cakephp 2 & 3 both. if I see sql query log then before inserting new record/updating selected record, save method call exists method first. what is need of that? as I am sure if its new record or exiting record.

I know this may be weird but I am sure that I am creating new record into system or updating selected record into system then can I by pass this check? I do not want to fire additional query.

is it possible by passing any parameter? or I need to make changes in core library.

Please advise.