Input limits are the maximum and minimum values you expect to measure, after any scaling, including custom scaling. Input limits are sometimes confused with device range. Device range refers only to the input range of a particular device. For instance, the device range for a DAQ device might be 0 to 10 V, but that device might be used with a temperature sensor that outputs 100 mV for every 1 °C. The input limits in that case could be 0 to 100, with 10 V corresponding to 100 °C.
Input limits in a smaller range can improve the precision of your measurement. If, in the previous example, you knew that the temperature would never be higher than 50 °C, you could choose a minimum value of 0 and a maximum value of 50. The device can then detect smaller differences in temperature because it is digitizing a voltage between 0 and 5 V, rather than 0 and 10 V.