Re: current and voltage
The mos gate has no DC current, but it has AC current flow when charge and discharge. And the long metal line cause a resistance connected to the gate, and this resistance combined with the parasitic capacitance from the gate to AC ground (such as the common source differential input pair) will cause some AC problems if it require high frequency performance. And also the metal line itself has its parasitic capacitance, which will also cause AC problems.
As for the anntena effect, it means if in your layout the mosfet gate is connected to a large area of metal 1, then in the etching process of the metal 1, large amount of charge will connected by this large area of metal 1 and cause a highvoltage on the mosfet gate, which will cause the gate oxide breakdown. So when layout , you can break the metal 1 and use metal 2 as a bridge over the metal 1, and thus avoid the high voltage on the mosfet gate.