SN74LS240 unused pin

Section 3 of Designing with Logic (SDYA009) says:

In many cases, functions or parts of functions of digital logic devices are unused, for example, when only two inputs of a triple-input AND gate are used. Such parts should not be left unconnected because the undefined voltages at the outside connections result in undefined operational states.
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As a result of the input circuits of bipolar devices, a high level is established at open-circuited inputs. The voltage at such an input corresponds to the threshold voltage of the input circuit (about 1.4 V or 1.1 V with devices from the SN74LS family).

Fairchild's Designing with TTL (AN-363) says:

Inputs are usually tied to V_CC through a 1 kΩ to 5 kΩ resistor, since tying them to ground means supplying the I_IL current instead of the I_IH current. I_IL is several orders of magnitude greater than I_IH . The resistor is recommended to protect the input against V_CC voltage surges and to protect the system against the possibility of the input shorting directly to ground. A single 1k resistor can handle up to 10 inputs.