Expressions can seem really daunting. But faced with their ability to help us simplify/automate work and safe-guard against future changes, it makes sense to start using them. Even though approaching expressions can be intimidating, think of them like After Effects itself: You can do very powerful things with a very basic understanding and what you can do only grows the deeper you dig into it.
Above is a tutorial that goes through a very simple example for creating an animated bar graph and building it with expressions so updating and re-using are easy.
0:00 – Introduction
1:10 – Creating Animated Bar Graph
11:28 – Baking expressions into keyframes
For Text Layer:
parseInt(/* pickwhipped property */) + "%";
For Bar Graph Layer:
var num = /* pickwhipped property */; var h = num * 1.2; //adjust by a ratio value [value, h];