The question with visualizations is: what do they actually tell us, in what way are they helpful? They are well suited for providing an overview of large amounts of data and their functionalities will surely be enhanced in the future. However, we should always be aware of the imperfections arising from OCR or metadata glitches and of the limits of such a visualization.
By way of example, the Ngram viewer doesn’t account for changes in semantics of words (or for disambiguation, for that matter). Terms are likely to have different meanings at different points in time. Nor does it tell you more about the cultural context which may be crucial for understanding the distribution of highs and lows in the graph. Counting occurrences is not enough to reflect semantic drifts or contextual information.
All in all, here’s another example of “computers only process symbols” – it’s up to people to create meaning from the results. On the other hand, we wouldn’t be able to explore the abundance of data without such analytical tools.