Good morning, Andy J Hart;
You pose a great question. The Gospel and presenting testimonies are two types of ministering and complement each other.
Preaching the Gospel can be salt and light to the person who is listening and needs to hear. Presenting a testimony can also minister to the person who is also listening and needs to hear.
I have witnessed both, leading to an altar call. The person coming forward desires to make a confession of faith or renewed commitment to Christ, and it's a blessing to see one or more join the person in prayer and support.
God bless you, Andy J Hart, and thank you for sharing.