I'm not saying people will spam them with "empty" commits, but in the same way that programmers all have their own unique writing style, people have their own habits and work flows.  I've definitely heard people  say things in the past like "we need to commit more, our graph is low this week". Committing more in these cases is just an aesthetic, superficial thing to "look" more productive, and has little to no effect on what extra work actually got done. 


It's a good metric for viewing activity, however it can be easily faked (not specifically by sending empty commits, but committing every 20 minutes instead of 2 hours 6x's commits for example), and it also excludes off-Github work (NEO, for example, has a very plain Github when you just look at the official github. However, if you dig deep, you can find the NEO dev's on a separate repository writing hardware wallet code months before they were supported by Trezor Wallet, that they get zero Github recognition for  it because it was done on the non-official github. This results in work being untracked, deflating the numbers, but despite the work being done, the product was advanced regardless).


Regardless though, it's still a cool metric. If you have a very diversified portfolio, this link is definitely useful to find which coins just have a dead team that isn't moving forward. It's hard to manually keep track of every project lol