You can refer to this article! Garbage Collection and Memory Leaks in Roblox - What you should know - Resources / Community Tutorials - DevForum | Roblox
Memory leaks are information that isn’t being used, it’s best to prevent them because they can take up memory and while they may not be much of an effect by theirself, if they stack then performance will most likely be a large issue. you can probably prevent them by scripting in methods that wouldn’t leave excess instances that are no longer being used
that’s my rendition, but the article above explains it much better than me