There's a thread on zellbriggen in the roleplaying board as well, started by myself.
http://www.classicbattletech.com/forums/index.php/topic,2811.0.html
Personally I find zellbriggen a bit odd. In your average battle for example a force with tanks or infantry which are not bound by zellbriggen can basically do anything they want and mess up with the whole battle while still acting within the rules. Furthermore you get other reports about clans either not adhering to zellbriggen (against hated enemies) or using perversions of traditional zellbriggen (ie Ice Hellion where a star of light mechs duels against one).
If you want tactics, in my thread for example the writer said that a person could potentially duel stars or higher formations against one another. So a cluster could duel a cluster, and within that battle duels may not be adhered to. Which goes somewhat against the waste not, want not mentality, but with some clans it may make sense. Burrock and Blood Spirit aren't going to adhere to zellbriggen when fighting each other, neither is Blood Spirit vs say Star Adder.
To me it's always seemed that it's the ideal form of combat, but that many clans quickly throw it away with any convenient excuse if it suits them.
In another way, zellbriggen and bidding in general is just a convenient way to make battletech battles more meaningful. There's a reason why in 3025 a single lance or a company could conquer an entire planet. For that same reason, a single star of omni mechs can be used to fight trials of possession for some genetic legacy. It's because that's the size of most battletech games! The designers want to make the battles' actions relevant, rather than an abstraction of what is really going on or a smaller part of a greater whole. That would be my assumption anyway.
You can take a lance on lance and have a small meaningful battle. Or you can have a star vs star or even mech vs mech and have it mean a great deal. A person doesn't need 30 mechs on the board and a large group to have a battle of any significance.
1. Vehicles and conventional infantry are very rare among the Clans (with a few exceptions). The places where they are concentrated the most are usually in enclave garrisons, and the attacking commander should already be prepared for them to be included in the defender's bid.
2. Vehicle crews and infantrymen, while they aren't bound by by zellbrigen like other units, are still Clan warriors and thus adhere to the concept of honor. Sure a tank crew might be able to "mess up the whole battle," but they would likely not shoot an already-dueling opponent in the back, for example. That's not exactly honorable. But will they attack an already-dueling unit head on if they have a good shot? Absolutely.
3. Throwing away zell when confronted by hated enemies? Certainly. Zellbrigen is only used when fighting
honorable opponents (unless you're a Star Adder and use zell against EVERYONE, even on bandits). For example, if you're a Ghost Bear, those Hell's Horses have NO honor because they killed one of your Clan's most beloved Khans while he was
in the middle of giving a speech. That's just
rude. Similar examples underscore the bitter rivalries between other Clans.
4. The Hellions' concept of honor is a bit different than other Clans due to their evolution of tactics and 'Mech options. They send 5 'Mechs against a single target, and the first Hellion to score a HIT is considered to have "won" the duel, even if they get shot down later.
5. A whole Star dueling another whole Star or an entire Cluster dueling another Cluster en masse just does not happen. The essence of Clan combat is the one-on-one duel, and that only devolves into a melee once someone breaks the rules. For a Star-on-Star or Cluster-on-Cluster duel to occur outside of a Hellion-on-Hellion Trial, these engagements would have to
start out as melees from the beginning, which would imply both groups went into combat with the idea knowing the rules were already broken, and no honorable Clan warrior is going to stand for that. And a Cluster-on-Cluster "duel" wouldn't really work, seeing as how a Cluster's component Binaries/Trinaries are likely spread out across a large area of terrain, and thus the scale wouldn't really work.
6. Small Clan vs. Clan engagements aren't purposefully small to "make the actions meaningful." They are small because they
minimize casualties and thus reduce waste.