Most android phones always need a restore at some point, due to apps that can cause instability or other issues. If you want to fix issues with your LG Mach, then factory restore is the way to go.
If you are experiencing problems with your At&t LG Optimus G, then you may want to perform a hard reset. Some people experience lag, freezes etc and doing this often works to fix the issues.
If you are experiencing issues like freezes, lags or unresponsiveness with your Spring LG Viper, then you should consider either a soft or hard reset.
To perform a hard-reset.
Turn the power off.