There is No "Inner Journey", its an "inner/outer journey", as it's always been, nothing new. You will have to continously negotiate what you deal w/ physically w/ your ideals, beliefs etc. So I don't really Believe there's a "vs" between the Two. :$
But, other than that, I guess it's to Prep yourself for the Outer Expression/Existence etc?
It will help you hugely, it will assist in you in decision making, it will show you the consequences of your actions before you make them, it will guide you to the great order of this world, Hukam, it will show you that the base actions that result in pleasure can be eclipsed by the most potent and enveloping pleasure in the world, the state of Naam, a state of connection with everything that contains Creator, you will end up not a slave to pleasure, but the owner of pleasure, and everything that you do to give yourself this pleasure will be in the order, in Hukam, you will live as Creator envisaged you should live.
Alternately, you could throw yourself in the sea of lust, anger, material gains, intoxicants and end up in bondage for the rest of your life, miserable, wanting and lost
It is not a question of the inner journey changing your life, but through Sikhism, that inner journey IS your life.
One can make journey only by boarding in some sort of Vehicle.
Without vehicle no journey is possible either inward or outward.
So get the knowledge of the Vehicle for correct destination and Board in ,Your journey would start.