* CPU: Compression will require additional CPU processing power (more for higher levels).
* Network bandwidth: The lower the bandwidth, the more sense it makes to enable compression.
In the table above, one might already notice the reduction in time is not linear to the reduction in data amount. Take level 0 and level 9 for example, the time is "only" cut in half even when the data amount is reduced by 85%. These were tested with a 54Mbps bandwidth. Once we did our tests again with a 450Mbps bandwidth, the time reduction is even less (less than 6 minutes v.s. 3 minutes). If the bandwidth increases further, e.g. to Gbps, the time reduction might become negligible. Combined with a weak CPU, it is even possible that the time is will be increased with higher compression levels.
Therefore, there is no general rulebooks for whether to turn on compression or not. The safest approach is still to try out different settings in the real setup.