It can and is a very effective method for witnessing if done correctly and then most importantly followed up on. What was it, back in the early to mid 70's when it was the hottest thing in the Christian life.
What better way to go into all nations than into one's home! Where we fall majorly, is in the follow-up. We go, we share, they accept, we leave! They....? We don't know, because we never see them again. We only partially do our job.
I think back at those times when I would be with a group from church out witnessing and can still feel the Spirit in the air, being all fired up for God.
Mary just hit it on the head when she said what she shared was only part of her salvation story. Amen sister!
Error does not become Truth because it is widely accepted; Truth does not become error, even when it stands alone!