If you have a 150w+ TDP gpu which obviously requires good cooling, you need the front fans to push in cool ambient air for the gpu. That's 1 point to keep in mind.
If you have a heavy oc with 1.3v+ vcore voltage and power draw more than 150w, your mobo vrm will be taxed to give that stable vcore voltage and stepping down all that wattage. So in that case, you need a top intake fan to cool off your mobo vrm heatsinks.
In some cases, you need both ur gpu and cpu to run at peak performance. In that case, the pc O11 dynamic case offers both possibilities. Have your 2 bottom fans as intakes for the gpu, 2 fans in the top as intake for mobo vrm cooling and side mounted aio exhaust for the cpu.