I once asked Albert Mohler what his thoughts were on the invitation/altar call. He said it felt it was necessary yet dangerous. Here are 9 points on the subject from the great Dr. Martyn Lloyd Jones from the book Preachers and Preaching, Zondervan, 1971, p. 269-279)
1. It is wrong to put direct pressure on the will. The will should always be approached primarily through the mind, the intellect, and then through the affections. The action of the will should be determined by those influences.
2. In the end it may produce a condition in which what has determined the response of the man who ‘comes forward’ is not so much the Truth itself as, perhaps, the personality of the evangelist, or some vague general fear, or some other kind of influence.
3. The preaching of the Word and the call for decision should not be separated in our thinking.
4. This method surely carries in it the implication that sinners have an inherent power of decision and of self-conversion.
5. There is an implication here that the evangelist somehow is in a position to manipulate the Holy Spirit and His work. Some organizers today even predict the results.
6. This method tends to produce a superficial conviction of sin, if any at all. People often respond because they have the impression that by doing so they will receive certain benefits.
7. You are encouraging people to think that their act of going forward somehow saves them.
8. It raises the whole question of the doctrine of regeneration. This is the most serious thing of all. This work is the work of the Holy Spirit, and His work alone, no one else can do it. And as it is His work it is always a thorough work; and it is always a work that will show itself.
9. No sinner ever really decides for Christ.