It is highly advisable or should i say, MUST do to make the side
panel fans as intakes rather than exhausts.
The nature of hot air inside your case produced by different components
installed is to rise up and it would be difficult for those hot air
to exit on the side even though it was being suck by those side panel
fans converted as an exhaust because before it goes through
the side, the majority of hot air will just be sucked again by your
procie and video card cooler fans, so most of the hot air will just
recirculate again and will cause your system to run more hotter than usual
specially if your have a highly oc'd procie and video card.
That is why if you notice the best enclosures around today
specially for gamers and enthusiasts are designed
with their exhaust fans placed topside (usually two 120mm fans
or in single of 140, 200 or 230mm fan) and the other is on
the rear side (usually a single 120mm fan) placed slightly on upper
part in parallel with the mobo's external ports.
This is to make the hot air inside your system leaves naturally and easily without
any distraction or disturbance, since it rises up, helping those hot air exit
based on its behavior would add to the enclosures cooling performance
and efficiency.
In general, since cold air can be sucked easily through the side
panel intake fan(s) and or though the front intake fan(s),
hot air is easily replaced by cold air thus resulting a high air flow.
-- This means your internal components are provided direct cold air
all the time which they need perform better and to last longer.