I installed my CPU cooler and it is too tall for my case, so I have to leave the side panel off. Is this a bad thing? Are there any types of precautions I should take?
As long as you don't have any young children or pets who might get into it, you should be fine.
I have a cat, though I have the open side angled towards my desk and wall.
i will say it prevents you from having positive or negative air pressure, so basically the only air thats gonna be movin is whats directly affected by the fans. it's not optimal, but it doable. just make sure you have airflow over ram, NB, SB, ect. ..
aka, just watch out for hot spots
It's actually a bad thing. Like above, it prevents any sort of air pressure from being able to form inside your case. While it is true that the ambient temp might become cooler, on a hot day it's going to be problematic and you are going to have dust build up, like alot of dust.
You know how if you leave stuff just lying around for a couple days without moving it, dust gets all over it, well that's what is gonna happen. You prevent this in a case by having a sealed environment with positive air pressure to keep dust from passively flowing in. I recommend just going for another CPU cooler.
...you'll havemore dust than under your couch
(you said you have cats- look under your couch and chairs and desk and you'll know what I mean)
what kind of cooler is it and how much does it stick out?