They did an item in my hall a while ago about the importance of informal witnessing. Everyone had to put their hands up to show how they came in the troof. About 40% were born in, 40% came in through 'informal contact' & only 20% through door2door.
Formal preaching is IMO now just busywork for witnesses. It serves the purposes of; constant reinforcement of your belief system through trying to foist it on others, self satisfaction in varying amounts as to how many hours you put in & a method to make yourself visable to elders for promotion/reaching out purposes. It also allows single by circumstances or choice people to catch up on gossip in a self righteous manner & it's the only method by which single women can gain any status within the organisation. - They even make sisters wear headcoverings when sign-language translating these days.