It's when you have accumulated bitcoin successfully to a stage of overall accumulation that you can consider slowing down or considering the withdrawal systems.
Yep. .it makes more sense to make sure that a guy is withdrawing from extra bitcoin rather than if he were to still be accumulating and he is withdrawing prior to having had reached overaccumulation status.
Talking about that, it makes no sense that one would withdraw from their portfolio when they're yet to meet their target, doesn't show discipline, one of the features of a long-term holder is discipline and if one has set their target to accumulate a certain amount for a decade or more then the person should ensure they stick to the plan, aim at reaching their goal by continous accumulation without withdrawal then like you said, he can choose to withdraw from the extra accumulated coin. I also want to add that people shouldn't mistake slowing down for a pause or end of accumulation in their portfolio it's simply means that you can reduce the rate of accumulation so far you've met your target, for instance if you were accumulating aggressively before reaching your target you can decide to go slowly after you've achieved your goal and not stop entirely.