A high level of active share demonstrates that the fund manages a truly distinctive portfolio. The only way that the fund can outperform a given benchmark is by taking positions that differ from those in the benchmark. Active Share measures the percentage of fund holdings that is different from the benchmark holdings. Higher the active share ratio, greater is the divergence from the benchmark. The fund manager deploys active strategy to outperform its benchmark in the pursuits of achieving higher risk adjusted returns for the investors.

The mutual fund portfolio which has active share percentage more than 60% is considered to be an actively managed mutual fund scheme.

The Portfolios with low active share, need an extremely large outperformance from the active components to achieve the same outcome as compared to portfolios with a relatively higher active share.
To top it off, fund managers that run closet indexing or index hugging portfolios/strategies need to also account for asset management fees and dealing costs which eat away a good part of investor returns. Imagine a fund that mirrors the index to the extent of 70-80%, the return will likely mirror the index and then once deduct a 2.25% total expense ratio, underperformance is inevitable. Index hugging is a classic recipe for consistent underperformance.