What is the true point of 'engagement'?

Apparently, it is to give you time to prepare for the wedding but does there need to be such a fuss. why can't it be that the couple just tells people that they are in getting married in for example march and start planning instead of gettin an engagement ring and usin the proper term of 'fiance' while engaged. If am being extremely cynical, i would think its just a ploy for the ladies to get a ring.