Agreed. Front and sides draw cool air in, back and top exhaust hot air out. Generally you want front to back flow. If you have "blow hole" fans, and since heat rises naturally, top fans help with that. I have not seen a case with bottom fans, but to help the natural flow of heat, they would draw cool air in too.
That said, you generally want "flow" through the case where, normally, the only turbulence desired is directly on top of the CPU. I have seen "system" (motherboard/chipset) temperatures rise with the use of a side panel fan because it either disrupted that "flow" through the case, or disrupted the cooling effect across the chipset from the CPU's HSF. Some cases use a tube to direct side panel air to the CPU so it does not disrupt case cooling.
My point is, monitor all your temps carefully before and after and if the side fan does not help, don't use it as it will be a waste of energy, it will suck in more heat trapping dust, and it increases noise levels.
Finally, you can have too much air being drawn in causing an over-pressure effect. If you don't have enough vents or exhaust fans, this pressure actually causes the air to stagnate - or not move. And that means not enough "flow" to move the hot air out.