Most large companies beat most quarters, because guidance is set conservatively and analysts anchor to it. A small beat is therefore close to information-free, and shares frequently fall on one.
The reaction depends on the quality and the outlook. A beat driven by a lower tax rate with guidance left unchanged is worth little; a beat on volume with a raise is worth a great deal.
Example: Northwind Tools reports $0.99 against $0.98 consensus. The one-cent beat comes entirely from a lower effective-tax-rate, revenue misses slightly, and the shares fall 4%.
Related: consensus-estimate, earnings-miss, guidance-raise, whisper-number, earnings-report