When applying staggering reveal animation effect, suppose you have hundred letters and you want to apply this effect using custom css. Now it's not that hard but it's a lot time taking. First you would have to put each letter in different p tags, means 100 p tags. Now you would have to give a unique id to each of them, means 100 unique ids. And when animating you would have to animate 100's of them individually and suppose you have to change just 0.1s delay then you would have to change delay in 100's of them.