Hmmm....looking back over the course of my ministry, probably about 75% in favor of knowing in advance. The times you don't know about can be hallelujah moments. I think of two churches where two different deacons came forward and apologized to the church for sinful behavior and asked for forgiveness. One church I know of that has no invitation sees this kind of thing all the time. People ask for time to confess sin publicly, apologize to people, etc.
One thing I caution here: never call a person forward whom you've talked with earlier. My rule of thumb: if the person doesn't move, I don't move for them. Filling in for my home pastor for an extended time, I was approached by a stepdad. He said his stepdaughter had accepted Christ and wanted to be baptized and said she would come forward at the next service. (She was unavailable to talk then, and I planned to talk to her before the invitation to see what had transpired). Next worship service, during the invitation, no movement from the family or the girl. The service concludes. At the end, he kind took me to task, expecting me to call her down to the front. I explained (again) that I don't do this, that this can create a false sense of security (I've heard many times "Well, I must be saved, the preacher even called me to come forward...). And that we should talk then and this could happen next service. He didn't seem satisfied. The pastor had my back, as he doesn't do the same thing. I'll let you decide how it turned out. She was never baptized and has never publicly made a profession of faith and now is living a rather gross life of sin. Apparently, she was pressured into some sort of prayer regurgitation to get her stepdad off her back and never really trusted Christ to hear her tell it. So do be careful.
There are times it helps to have your ear to the ground and use wisdom. I caught wind in one church I filled the pulpit one Sunday that a member was going to use the "Does anyone have a word to share?" portion of the invitation to blast a fellow church member who she had a grudge against, and try to provoke an altercation. Long story short, I was able to nip that in the bud. Who knows what would've transpired if she'd been given the floor. Shepherding means protecting sheep.