I’m not talking about high detail meshparts. If I were to change every basic part into a meshpart (they’d all have the same mesh id), would there be a problem with lag?
In my scenario, would it matter if I were to use meshparts over parts? If so, can someone actually explain how one might be worse than the other?
i would say mesh parts are better than real parts idk the reason but i have seen very big difference in lag when using meshparts than real parts
Use them when needed, using too many meshes or to many parts can both be bad but it depends on your situation. If you have complex objects you might want to use meshes but if you are making buildings you might want to use parts.
Thought it’s an unrealistic scenario, a square MeshPart is technically slightly worse for performance than a square Part, since the MeshPart still has to download even simple geometry to the Client. Part geometry is already included on the Client.
Again I want to stress that this comparison is flawed since this isn’t typically how MeshPart’s are used in normal workflows. You can’t compare any one object directly to another object without acknowledging the complexities 
Thank you for responding! I didn’t know some of what you said and my apologies for the bad comparison.
I do have a question about this though;
What exactly will happen if I use meshparts over normal parts? Will it just be slightly longer loading times or will it slow down framerate? (if it does anything else please let me know)
It’ll theoretically slow down load times and have a negligible change on rendering. Theoretically, only because I’ve never actually seen it done because there’s no reason to not use Parts in this very specific situation.