There's no real need if all seems well now.
Makes sure the app can't update automatically as eventually things might get incompatible with older firmware.

"Best Advice" is go for all latest to have most bug fixes and features.
Alternatively stay with what works for you now. 
Updating one part of the system without doing everything can lead to problems. 

Phantom 3 is a relatively mature platform and what's latest now will likely be how it stays unless they feel obliged to introduce further lock-down technology.