For example, losses on the international portfolio could be harvested to offset gains on, say, a small-cap portfolio. This would need to be implemented in such a way that it doesn't undermine the portfolio's asset allocation. The lesson is to be as holistic as possible about tax management, and not to be narrowly focused on just one part of the portfolio.
While none of these techniques is especially difficult to implement, they do require a dedicated effort; and few investors or asset managers use all of them rigorously.
Earlier, we mentioned indexing. The main way indexing, either through index funds or index ETFs, is tax efficient is deferral of capital gains. In other respects, indexing lags far behind systematic tax management as it gets no benefit from loss harvesting.