If Germany had won a decisive victory it would have been able to enforce all of its war aims.
You would have a similar situation you had with the Germany mastery in Europe in 1940 or the French mastery in 1811.
France would lose her great power status and be crippled in some way, eg by having to demilitarise and pay large reparations.
Belgium, Romania and reduced Serbia would become satellite states.
Poland also would become a German sattelite. The Baltics would be annex outright. Belarus and Ukraine would become German colonies.
Ottoman Empire would keep its hold on the Middle East and annex the Caucasus.
Austro-Hungary in my opinion would survive the war, but soon enough there would arise great internal turmoil. Depending on the severity of it Germany might respond by annexing Cisleithania and letting the Hungarians have Transleithania.
The German military would launch an expedition to remove the Bolsheviks from power in Russia and to in their place install their puppets. It would either cause the Russians to rally around the Bolsheviks, or more likely the Germans would be initially successful only for there to be rebellion of the patriotic forces against the puppets soon after.
In general I think this redrawing of borders and relations in Europe would be quite volatile and ultimately unsustainable. I think France would reconcile itself to not being a power and remain broken, but all accross East Europe there would drag on a low intensity conflict of basically everyone against the Germans and the Hungarians. Depending on how Germany chose to deal with it (it was very brutal in quashing resistance in its African colonies ) it could turn very ugly.
Versailles borders receive a lot of flak, but the borders as drawn at Versailles were on the whole much more just than the borders as they existed before World War I. Also they were much more just than what borders would be drawn in the event of a German victory. (With exception of course, in Macedonia, Alsace…) If you think the dictated peace of Versailles was bad, just take a glance at the dictated peace of Brest-Litovsk. (And no, it was not meant as a temporary settlement.)
Anyway yours is a strange question. Why the outcome of WWI mattered can not be answered in general terms. Once embroiled in it its outcome was important for the Belgians or the Serbs, the Bulgarians or the Turks, but it was not important at all for the Argentinians, the Chinese or the Americans.