What are the advantages of spreading Corps into two or more detachments versus keeping them concentrated in a single stack? Why make detachments of a single or two Corps, when I can just concentrate them in a single Army stack and just steamroll forward toward the main objective, sacrificing flexibility in favour of overwhelming force?
I see it often over maps on AARs, but aside of covering more ground and frontage in trench warfare (which to my mind is the sole benefit) doesn't it open the possibility of being destroyed in detail, one by one, against a single Army stack? I see no benefit in risking getting one or two Corps destroyed against a super HQ stack just to cover a small town or a railway one of two regions away.