Don't think of Litchi as a replacement for DJI Go.
DJI Go is great but Litchi has some additional features and is particularly good at waypoint missions..
Use Litchi if you need the features it adds.
Using Litchi doesn't void your warranty ... but Litchi does not produce a log that DJI will consider to investigate an incident.
So if you lose the Phantom and DJI cannot study the internal recorded data from the Phantom, you could be on your own.