El gatillo rápido puede ser bastante peligroso y dejarte sin munición ante caídas continuas y prolongadas (donde un rebalance estándar tendría mucho mejor comportamiento), pero la otra idea que planteas tiene más sentido y ha sido tratada incluso por William Bernstein, él lo llama "overbalancing".
Un resumen de sus comentarios sobre el tema en su libro The Intelligent Asset Allocator:
"Before proceeding further, let me be clear: Adherence to a fixed policy allocation with its required periodic rebalancing is hard enough. It takes years to become comfortable with this strategy; many lose their nerve and never see the thing through. You cannot pilot a modern jet fighter before mastering the trainer; likewise, you should not attempt dynamic asset allocation before mastering fixed asset allocation.
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Think of it this way—when you rebalance your portfolio in order to maintain your target allocation, you purchase more of an asset that has declined in price, and thus gotten cheaper. When you actually increase the target portfolio weighting of an asset when its price declines and it gets cheaper, you are simply rebalancing in a more vigorous form—you are “overbalancing.” A simpler way of overbalancing is to increase your target allocation ever so slightly—perhaps by 0.1% for every percent that the asset falls in value, and vice versa.
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Rebalancing requires nerve and discipline; overbalancing requires even more of both of these scarce commodities. Very few investors, small or institutional, can carry it off."
También hablaba algo sobre ello en este artículo:
http://www.efficientfrontier.com/ef/703/timer.htm
"slow and relatively slight changes in allocations based on valuation and expected return. This latter strategy, involving very small and infrequent policy changes opposite large market moves, more often than not improves overall portfolio performance.
The latter concept is a bit difficult to grasp. Think of it this way: even the most devout efficient marketeers rebalance; trimming a portfolio back to policy is nothing more, and nothing less, than a bet on mean reversion. Taking the process one step further and adjusting the policy allocation itself opposite valuation changes is merely a way of amplifying a rebalancing move—"overbalancing," if you will.
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the judicious adjustment of policy allocations according to expected returns—increasing an allocation slightly when its expected return is very high, decreasing an allocation slightly when it is very low—will on average slightly enhance long-term results. This is simply an amplification of normal rebalancing.
Varying allocations—"timing," if you will—is similar to the consumption of alcohol. It can either enhance or degrade portfolio health; it all depends upon the circumstances and the quantity. When partaken in small, infrequent amounts from a concave vessel, its benefits are small but perceptible. When chugged indiscriminately, it is deadly."
