“WHY”: It can help you plan for the best places to sit, take photos, etc.
A friend is planning an event this summer and wanted to find a shady spot in a large park for people to sit. I remembered seeing this project, and it helped in my use case
Here is the website: https://shademap.app/
Here is the developer’s GitHub with some code, API, and sample projects: https://github.com/ted-piotrowski
Here is an article I found by Bellingcat talking about the features: https://bellingcat.gitbook.io/toolkit/more/all-tools/shademap
There is also this other tool ShadowMap (app.shadowmap.org), but the data quality wasn’t great for the places that I tried.
I used the tool when looking for a house to buy.
I was looking in a mountainous area so the amount of sun a house gets in winter can vary quite a lot. Even a few hundred meters can make a huge difference in some cases.