I see a lot of circuits where a capacitor and resistor are in parallel. I understand that this causes the capacitor current to be 90 degrees out of phase with the resistor and the rest of the current source.

I don't understand why this is useful in either a DC or an AC circuit. I ran it in a simulator, and it seemed to cause slight gyrations in a DC circuit (very slight), but beyond that I don't see what it does. Even with those slight gyrations, I don't see the practicality -- especially when the capacitor just branches off enough to be parallel and then is fed back in on the other end of the resistor.

Any help is appreciated.

Thanks.

 

Can you post some of these circuits?

 

Ok a small practical example using this circuit in DC you can create timers,on very simple terms, let fully charge a capacitor,the capacitor will hold the charge until it gets any path to discharge ,now lets add a high value resistor in parallel with the capacitor now it gets the path and it starts discharging but slowly and the time taken to discharge is what we use practicality in different circuits may be a timer.Their are lots more but what ever ,this is a very usefull circuits.

Good Luck