Does implementing fog affect performance?

Hello,
I am currently trying to get the best of unity engine’s effects, however I noticed that there was almost no fps drops just before adding the fog effects. After applying those, while playing in the editor, I encountered a lot of lags. Now my targeted platform is a general desktop system with 2gb RAM and an Intel graphic card. And judging by the system specifications of my Lapto(16gb ram, 4gb Nvidea GPU, I5), I think it’s a really bad idea to add those. My question is, while I was playing the game there was a green-ish loading bar on the Unity’s icon in the taskbar, showing that something must be going on in the back end, I wish to know what it could be, Could it be that due to that process, it was lagging a bit?, and will the lag be reduced once I remove the extra assets and files from the assets folder and I build the project with the fog effects?

I just wish to know how much restriction should I keep to make sure that my game behaves properly with the targeted platform.