Trying to make a better perfomance of my website and considering both sever loading (to admin) and browsing speed + convinence (to user). I'm getting confused with the setting of session function and autologin hack.

How to make a optimized setting to improve site accessing and browsing speed without increase server loading too much? Will the autologin hack eat a lot of resource if there're always many online users entering with it? If sever loading is the main concern, should I keep any of them?

Any suggestion will be appreciated.