Slack does not contribute to the insurance charges as it is not for buying of any coverage. It is more to built up the cash value in order to sustain the policy longer.

You may increase or reduce the slack as you wish.

However for any Reduction, you will need to sign a policy sustainability form that the policy may not be able to sustain as per in the initial quote.

Benefit is that the cash value in the policy can be more as compared to policy without the slack.

Also, if a payor or waiver is included in the policy, if CI or TPD, then the waiver will kick in.

Ofc if you only look at it from the investment part and you have another vehicle that can generate better returns, by all means, go ahead... No right or wrong.