I use this bleeder valve with a pressure guage to check the pressureof my beer when its carbonating in the keg. Connect it to the gas in side of the cornie. I let off excess pressure every so often until it stabilizes close to serving PSI. Good for over carbonated beer.
If you prime your kegs to carbonate them you can use this to help monitor that fermentation. No more increase in pressure, means it must be close to finished.
Of course that's just me. Maybe I like things with guages.
Note: Photo from Norther Brewer website.