The hard reset function shall only be use if the device always freeze or becomes unresponsive. It can also be use when you want to sell your device to upgrade to a new smart phone. After the hard reset, the device will be a clean device just like it just got out from the factory.

Hard Reset of the LG Nexus 5 Steps by Steps Guide

1. Turn off your device
2. Press and hold the volume down key
3. With the volume down key held down, press and hold the power button
4. The boot loader will appear and u can release both button
5. Use the volume down key to scroll and select the recovery mode
6. Press the power key to enter
7. Press the Volume up key, then press the Volume down key to scroll to wipe data/factory reset
8. With wipe data/factory reset highlighted, press the Power key.
9. Press the Volume down key to scroll to Yes — delete all user data.
10. With Yes — delete all user data highlighted, press the Power key.
11. Device will restart
12. Once the wipe is complete, with reboot system now highlighted, press the Power key

The LG Nexus 5 is now reset and shall have to perform the settings again to setup as a new phone.