I'm a bit confused about the ground clip on oscilloscope probes. I have
read that it can cause a ground loop when the measurement circuit is
grounded to the same ground as the oscilloscope itself. Is the ground clip
only to be used when there is an isolated ground then?

I have been taking measurements from 12V car batteries and DC power
supplies. Should the ground clip always be used in these cases?

If I am correct the ground clip should not be used to measure between two
voltages as one would do with a multimeter (referencing a different voltage
in the circuit instead of its ground). It confuses me why I would not be
able to use the ground clip to do that. An explanation/link would be
appreciated.

Thanks for any advice,

David.