Variety is, in many ways, the opposite of unity. In some ways, variety is totally necessary in order to recognize distinct shapes and type (which also happen to be shapes). But it's more than that: variety breaks up a composition, relieving some of the monotony caused by extreme unity.
Unity and Variety to Achieve Content Flow
Extreme unity, as seen in the image below, actually inhibits eye movement through a composition. Breaking this unity with a little variety, demonstrating in the steps below, will help create better content flow and increase visual interest.






Variety in Type
Variety is an important concept found in type design as well. Within a typeface, a good variety of thick and thin, round and flat, or dark and light can give a single line of type a beautiful and pleasing rythym.


Remove the contrast between elements and you remove much of the variety, leaving only the varied letterforms – which areobviously necessary for legibility and readability:

Lastly, variety between typefaces in a single composition can also be a good thing...or it can be a complete disaster. A pairing of two typefaces can be quite complementary, and thus create a harmony between them:

But mix three or more typefaces and you've strayed way to far into variety territory and have thus broken unity:
