DeFit is useful to fake Google Fitness data, which makes for a quick progress cheat for games such as Pokemon Go that rely on that data.
Using DeFit with Pokemon Go
DeFit is useful as mentioned above to fake running activity data to the Google fitness service. Individually, this won’t be of interest to many Pokemon Go players. However, Pokemon Go uses that very same data to determine what you’ve done while the game is closed.
To make use of DeFit with Pokemon Go, this means that you’ll need to set the DeFit app up as recommended by it. This means logging into your Google fitness account with it and turning on the sync fitness data switch.
From there, you can then use the app to make fake Google Fitness data. Provided Pokemon Go is closed, this data will then be used by the app to determine how far you’ve been walking while it’s been inactive.
You can make use of DeFit to hatch eggs, and boost your total distance moved in Pokemon Go without actually going anywhere.

If it is used correctly, your distance walked shown on your avatar profile page will be updated. This makes for an easy way to check if it has been working for you.
Can you be banned for using DeFit with Pokemon Go
DeFit is safe on its own, as it doesn’t actually interact with Pokemon Go directly. The app sends data to Google Fitness, which Pokemon Go will then read from there, and act according to it.
You do still need to be careful how you use this. Pokemon Go will likely detect suddenly moving 1000km in an hour as some kind of cheat, or automatically ignore it regardless. Assuming you stick to smaller amounts of distance, this could well be a useful tool to hatch eggs while you’re stuck at home, or farming Pokemon candy by “walking.”
Just keep the numbers reasonable and you should be perfectly fine. There don’t seem to be any reports of Niantic banning people for using DeFit. With that said, it’s always best to be on the safe side if you’re not absolutely sure.
To get the app to work, you must be absolutely sure you set up your connection to Google Fitness. Without that, the faked data from DeFit doesn’t actually go anywhere, and Pokemon Go will never read it. Just remember that this app isn’t directly a Pokemon Go cheat. As such, you’ll need to do that bit of setup work for it to function as one.
And seriously, close Pokemon Go while using the app. Pokemon Go will only rely on Google fitness data it can’t get data itself, which means it needs to be closed.