An external circuit often includes a series resistor and clamping diodes on the inputs. Leakage current through the diodes will cause a voltage drop across the series resistor, creating an offset error on each input. This error degrades the common-mode rejection of a precision op amp, adding error to the signal. The ADA4177 provides OVP and eliminates that error.
For a detailed explanation of the trade-offs, along with test data, please see,
"Op Amp Input Overvoltage Protection: Clamping vs. Integrated"