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Malley’s statement is incorrect. Rebalancing the portfolio so that target weights are maintained (constant mix strategy) requires more or less constant trading and is likely to force the manager to provide liquidity which could result in poorly timed trades but generally supplying liquidity results in lower trading costs. Note that requiring liquidity is selling when others in the market are also selling or buying when others are buying (resulting in higher bid-ask spreads) while providing liquidity is selling when others are buying or buying when others are selling, which may minimize trading costs. Upshaw’s statement is correct – both rebalancing to maintain target portfolio weights or creating tolerance bands would require constant monitoring of the portfolio, although the tolerance band method is likely to result in less frequent trading