In general, charts in Google Sheets are really useful when you want to visualize data sets. Usually these charts contain legends/keys, titles, axis labels, and descriptions with them. The Sparkline function is a bit different as it only allows for a quick look at data trends via a mini-chart within a single cell. For a quick idea of what they look like see the bottom two cells in the screenshot below.
Here's a quick video tutorial by the Google Guru:
Here's a link to Google's own whitepaper on Sparkline.