Well this depends on the desired outcome and the goal of the client.

If you are trying to achieve strength and power, you would want to take a solid 5 minutes rest between each set.

This way we would allow for your energy stores to be optimally restored. If hypertrophy is your goal, 60 seconds would do the trick.

When wanting to build muscle it is important to recover but not completely.

Now, if conditioning is your objective, 15-30 seconds rest will deplete oxygen stores and will force the body to utilize oxygen more efficiently and increase red blood cells to provide more oxygen to the muscles.