The "unfinished" tiny line graph with no fill is actually closer to what Tufte meant by sparklines. He meant those to be placed in text, word-sized, along with words to help communicate better.

https://www.edwardtufte.com/bboard/q-and-a-fetch-msg?msg_id=...

I feel like many people use "sparkline" to mean "pretty graph." Those, frankly, lack the punch of a sparkline.