The first chart devotes too much of their ink to graphical apparatus, with elaborate grid lines and detailed labels

In the second much of the non-data detail is eliminated

That leads to a cleaner design that focuses attention on the time-series itself

Unambiguously locates the altitude in six separate ways

Any five of the six can be erased and the sixth will still indicate the height

Sometimes you don’t need symmetry

And you can save space by removing redundant halves

Can also serve a purpose in some cases

If there is a time dimension involved, to show a full circle for example

And, similarly, in map plots to go “once around the world”

Some example ways of increasing the ink-data ratio:

Doing away with too much grid lines (or making them thinner)

Not plotting axes beyond the data range

Not plotting unnecessarily many axis ticks

Do you need axes at all?

Can you integrate a legend onto the plot, should you need one?

Can you have multifunctioning graphical elements in your plot?

Simple charts often have a (very) low data density

Consider for example a bar chart with only two classes with only one value each (4 entries in total) that takes up considerable space when visualized

Maps, on the other hand, usually have a very high data density

Or other area plots, for example direct visualizations of matrices

Well-designed small multiples are

Inevitably comparative
Deftly multivariate
Shrunken, high-density graphics
Usually based on a large data matrix
Drawn almost entirely with data-ink
Efficient in interpretation
Often narrative in content, showing shifts in the relationship between variables as the index variable changes (thereby revealing interaction or multiplicative effects)