I just told you. The amount of customisability with the OS itself.
I was just asking what in terms of that you can do, I've heard the basics, just want to know more in-depth user based tricks etc.
Such as custom UI's etc. etc.
Well for starters, the Nexus 5 comes with a stock launcher (the thing that shows the home screens and app launcher) that offers very basic customisability. Basically, all you can do is add/remove pages and widgets/apps. Downloading a 3rd party launcher from the Play Store can allow you to go even further. Customise grid sizes for the home screen to allow more things to fit, customise icon sizes and fonts, have folders in the app launcher and even tabs and so on. The best two 3rd party launchers are Apex Launcher and Nova Launcher, which both look very close to the stock launcher so you won't lose the basic visuality of it.