Guidance is the forward-looking part of an earnings-report, and markets are forward-looking. A raise, a cut, or a withdrawal of guidance is frequently the main driver of the post-earnings move.
Companies manage guidance conservatively so they can beat it, which is why beat rates are high and why a small miss is punished.
Example: a company reports a record quarter but cuts full-year revenue guidance from $4.2 billion to $4.0 billion. The 5% cut produces a 15% drop in the stock.
Related: earnings-report, earnings-call, eps