It will do the Germans a huge amount of good compared to OTL. Forcing the British to react is a partial victory, because it consumes resources and hurts logistics. There are a lot of things that will help.
1) The UK will likely reinforce the English coast with extra land units. The British had an irrational fear of invasion based on actual threat levels. While not decisive, it helps the Germans in small ways by taking pressure off the Germans and increasing the German land reserve.
2) The British will still want something like the Dover Barrage in the English Channel. Since it is a lot farther from Cherbourg to England than Calais to England it will both consume more resources and be less effective. Small German Win.
3) Cherbourg is the Eastern most port the Entente will be able to use. More ships need, more rail cars needed. These assets will have to be stripped from somewhere, and this will hurt something else.
4) If the Cherbourg Barrage, or wherever chosen, is not strong enough, the U-boats in Germany will use the English Channel not the North Sea to get on station. This means more U-boats on station at any given time.
5) Air bases closer to England.
6) More agricultural land controlled by Germany. A little more food for Germany, a little less for France.
7) Industry - More areas for Germany to loot.
8) Britain may move a squadron of Battleships to Southern England. Less forces at Scapa Flow or some other theater.
Now none of this has to be a war winner, but it could be. Yes the English will react and counter some of the effects, but it will be at least a minor help and will extend the war. Even a very efficient reaction will have a noticeable impact. A few % few infantry and artillery in France. Less supplies due to longer transport times. The extra ships required to react to the extra danger come from somewhere. A lot would depend on the exact details of how it plays out, but it would likely extend the war by at least a couple more months, and could even result in a cold peace/draw type scenario.
IMO, if Calais happens in the initial Race to the Sea, Gallipoli will be cancelled which will have profound effects on the war and the UK is likely to greatly over react (due to public fears) and keep a lot of extra forces in England. There is potentially a chain of effects which will make it radically harder for the Entente to win the war. WW1 is not like WW2 which was a blowout. In WW1, Germany barely lost, so it does not take a lot to tip the scale.
Well visualised!
In a war where in later years the combattants were racing each other toward collapse and revolution this is the sort of thing which can change the balances and win/lose the war.