I've often found that the "alternative" combat system, the combat system adapted for AD&D and B/X, to be inadequate at times. There are situations where a mass of goblins or like creatures (in my case, redcaps) would be better represented as a single figure. It's just too hard to keep track of 10+ creatures/characters and forces play slows down significantly. Similarly, it would be nice if there was a faster way to determine the victor in higher-level combats. It just takes too long to go through 50 hit points or more before one side falls or retreats. In my AD&D game, however, my players, are still at too low a level for this to really be necessary at the moment, so I haven't had to deal with it much.
Chaimmail, the tactical miniatures wargame from which D&D gains its antecedence, has three combat systems that encompass differing scale of time and the number of figures represented. The three systems as the Mass Combat system, the Man to Man system (which is the closest of the three to the alternative combat system) and the Fantasy Combat table. Each of these three systems could be very useful in any given gaming session.
The Mass Combat system assigns each figure at troop type which determines its fighting capabilities. While the Mass Combat system is intended used for a 1:20 score, I've used it successfully to represent several higher level D&D characters fighting off a horde of skeletons without much difficulty (although it did take a little forethought as to how to do it properly). This method sped up play significantly so that we could get done with the encounter and back to the exploration.
The Man to Man rules are great for one-on-one combats and skirmish situations against human or near human opponents. This combat system creates a very gritty and tactical game that lends itself well to encounters with important NPCs. The Man to Man rules wouldn't be my go-to system for most combats, but for duels, gladiatorial matches, important skirmishes amidst a larger battle, and important battles you want to carry tension and weight I find them exceptional.
The Fantasy Combat table allows for a way to determine the victor of high level battles by a single die roll. I find that the Fantasy Combat table works best when used in conjunction with the Man to Man or Mass Combat systems. At its best, the Fantasy Combat table allows a hero to make an unlucky, last-ditch attack against a more powerful opponent with a small chance of killing that opponent outright.
That is not to say that there are no problems associated with the three Chainmail combat systems. The major issues I've found are that it is often tricky to assign troop types in the Mass Combat system; that some weapons (fails and two-handed swords) are vastly more powerful than others in the Man to Man system; and the Fantasy Combat table can often lead to anti-climactic results if overused.