Obviously, a great deal of the pleasure of wargaming lies in commanding armies on the tabletop. I would not be alone, however, in writing that I gain just as much enjoyment from planning and organising my forces before they ever face the enemy.
I'll be referencing Ancient warfare and the Hail Caesar rules specifically, but the points raised apply to most periods and (I suspect) most rule sets.
Before a game begins there are choices to be made: which units to include, and how they are organised. Do I add more bow-armed skirmishers and drop a Medium Infantry unit? Do I divide my army into three divisions or four? Do I spread my raw troops or concentrate them in one, lame, division? These decisions all have ramifications once dice are rolling.
I think having some grasp of points totals is important. In a meeting engagement, a degree of parity is usually desirable; in an assault scenario, perhaps the defenders should be stronger. Being able to add or subtract units to reach something workable helps avoid the dreaded "walk-over" — something no one enjoys. Points can be anathema to non-tournament players but I feel knowledge allows you to plan more interesting games.
Command abilities are another useful lever. Personally, I like fielding Roman armies with merely average commanders leading superb troops. It often produces more interesting and less predictable games.
Finally, there are "Special Abilities". Hail Caesar includes several pages of optional rules that enhance or restrict specific units and troop types. Are your Celts "Fanatics" (+1 to Morale rolls until Shaken)? These cost points too, and I like the idea of a limited "Special Abilities budget", from which each player selects what — and to whom — within an agreed cap.
I should note that HC has no official points system but there is a players' generated system that works well.
I can already hear the counter-argument: that historical commanders had little freedom to tweak forces — you took what you were given. That's true, but I would emphasise both syllables in "war-game".
I'd be interested in responses to some or all of the above, particularly how this plays out in your periods and your preferred rule sets.
