If it is something that needs to be done, it's completely fine to take the side panel of your case off. In fact, it is a recommended method by prominent tech YouTuber JayzTwoCents for keeping your PC cool in high temps:
https://www.youtube.com/watch?v=jjx9SE3QdTk
However, you do have some things to watch out for. One is that this way will probably induct more dust into your PC, which can slow airflow even more and clog up your PC. Dust is NOT good for a PC, so if you decide to do this until you get a better case (which is recommended in the long run), you'll want to dust it frequently.
Also, you need to make sure no foreign material ever gets in your PC, as this could ruin it. With no side panel on your PC, it is much easier for stray particles of, say, a liquid or food to get in the PC, and that could potentially ruin part or all of it.
Bottom line is yes, it's perfectly fine to do that as long as you are not completely oblivious to the way you act near your PC. You don't want too hot hardware, as that throttles performance and reduces component lifespan.