Well I will jump in here and also do some searching to be sure I get my facts right. You have basically 3 types of loads. Resistive, capacitive and inductive. A light bulb would be resistive, Some types of power supply's would be capacitive and motors inductive.
In a resistive circuit, voltage and current are in phase (most efficient)
In a capacitive circuit, voltage leads current (and varies as capacitance changes)
In an Inductive circuit, voltage lags current. (sucks up power and changes with drag on motors and speed and stuff like that)
these out of phase conditions can be monitored and that is why you see some shops with lots of equipment using motors also having banks of capacitors. The value of the caps combined with the inductive load brings the current - voltage phase separation back together making things more efficient. (helps keep the power meter from spinning out of its socket)
Sometimes you will see high voltage lines that run for miles, just suddenly criss cross each other. Power companies use the capacitance of the air space between the lines to help keep current and voltage close to each other. The ideal end result if I remember right is at the end of the transmission line they want voltage leading current a little bit. It helps reduce voltage line loss at the other end from the source.
Typically electric motor startups slingshot voltage - current phase shifts way far out of wack creating large current spikes. Thats one of the reasons they rate electrical devices in amps and HP. Also why they have capacitor start motors.
The formula for the above information is... ((Learned this when young + 35 years) / beer) - brain cells = I think I got this right.