They're amazing though! They make everything much simpler, and are more optimized than ugly circuitry :P
My Tardis has over 100 functions (don't remember how many exactly, somewhere around 120 I think), imagine how awful it'd be to work with that in block form! Also you know how annoying it is to have to insert a command in the middle of a chain when using command blocks right? Well with functions it's super simple, cause it's a text file with a function on each line :P