Closing loops or not? - supply lines on a PCB
The goal for a ground (or power) connection on a PC board is that to the extent possible, the instantaneous voltage is the same everywhere along its path.  This is a problem under two conditions: high current and high frequency, and a real problem when you have both, as in pulsed current.  So in general, you want to understand and control the current paths.  In your example, if the upper left component required high or pulsed current, the top example would have high resistance and inductance, and you would get spikes between various points on your ground.  With fast switching devices and high capacitances, these can easily have amplitudes in the hundreds of millivolts.  For low power circuits, the problem with closing the loop is that if there is EM radiation nearby from an external source, you will induce a current in the loop that can push around today's very low power devices.  So your approach should be to avoid loops and have a separate current path for high frequency or high power switching portions of your circuit, different from ground paths that are used for low power devices or for analog or digital reference voltages.