Biasing an inverting Op-Amp using a voltage regulator
You can use it to power other ICs (or other purposes) but keep in mind that the regulator has a non-zero output impedance (it's pretty good at DC but your other loads may have high frequency variations) and the regulator output voltage will thus likely vary more than if you had a dedicated regulator.
L7805 is based on a bandgap reference and is thus fairly noisy in itself, somewhere in the 300-400uVp-p range typically (10Hz-100kHz) with a 100nF capacitor on the output.
It's generally going to be superior to using a voltage divider off the power supply rail or a 5.1V zener diode, but not as good as using a reference IC.