Here is a practical application of the dual differential amp. This circuit is for DC or slow moving DC like Strain Gauge and transducer signals. The RC and Zeners are for protection and clamping. Why and how has been described in other posts here. The high impedance op-amp input cannot face the real world unprotected. OP07 is always the selection due to the low offset. When the sensor generates data in mV, you cannot afford any error introduced in this front end, right.