There is still a lot of talk regarding how to build the most ideal/balanced/overpowered divisions in order to counter AI and human opponents. The idea seems to be trying to build the largest divisions possible while maintaining width in proportion to 80 and min-maxing different firepower and defense stats to reach optimum versatility or specialization.
So is there any advantage in building Brigade-sized templates? These would not be the size of a "full" division and might only consist of one or two columns.
Definitely a role for battalion to brigade sized formations, especially when manpower and equipment constraints apply.
Experimental armored brigades early on
Police
Scouts
Coastwatchers
Port/Fort token or "dummy" garrisons
Various maskirovka purposes
Speed bumps- combat alerts you to enemy presence and gives you some time.
Cadre battalions (to be upgraded to a full strength template) - though this can be abused as can some template changes
Sacrificial pinning attacks to delay enemy combat or advance.
Colonial or other garrisons - weak infantry-only brigades are common in the colonies
Getting CAS into action - (Close Air Support requires a combat to join in.
Raiding to shut down enemy supply lines or facilities by occupying territory.
Main combat forces for countries with very little manpower
BUT if on the clock (as is normal in multiplayer at least) the above uses take valuable time so it may not be worth managing tiny units. which in HOI4 creates organizational clutter. Some uses take advantage of AI weaknesses. Having battalions, regiments and brigades skulking around may also annoy other players.
and good luck to thee, Emperor Batman, in your battle with the Emperor Penguin