Ease of use when it comes to finding information about vessels; also that they can be used for other purposes such as monitoring sea conditions or marine species etc.
The fact you need an app means if your phone runs out of battery then you're left waiting until it's charged before being able to continue looking up data! This could easily have been overcome by just having access via website instead - which would not require any additional software installed (which is likely more resource intensive) but I guess this was done with security concerns?