Yeah, there's a tradeoff for doing that. The case is preinstalled with 2 fans: a rear and top exhaust.
Starting with torture tests and the NZXT H500-only data, average CPU temperature was 61 degrees Celsius over ambient in the torture test and with the stock fan configuration. Again, as a reminder, that’s dual-exhaust.
Removing the unnecessary top filter lowered that to 57.3 degrees. It’s a good thing NZXT included the filter so that it could be used in top intake configurations, but if the stock (exhaust) fan layout is used it should definitely be removed.
We left the filter in place for all other tests since that’s how the case ships. Adding a 140mm intake fan to the uppermost of the front mounts lowered CPU temperature barely more than removing the filter did, down to 56.5C, while moving both 120mm fans to the front intake slots was equivalent to removing the filter at 57.2 degrees. Exhaust-only may not be the best stock configuration, but it does leave more room for CLC options in the front.
Average GPU temperature in the torture test was 52.4 degrees Celsius with the stock fan configuration, and 53C with the top filter removed, a minor change within margin of error.
Interestingly, temperature went up quite a bit with the 140mm intake fan added, up to 59.3C and 58.9C with the 120mm fans moved to front intake. This is where the the stock fan configuration starts to make sense.
NZXT chose negative pressure because this allows the GPU to draw air in through empty expansion slots, rather than relying on intake from the mostly-sealed front of the case.
When front intake fans are added, even ones pointing towards the GPU, this airflow pattern is disrupted and the GPU can no longer pull cool air in from behind the case.
Adding fans in the front of this case will lower average cpu temps, but gpu temps will actually rise.