If you are asking it for yourself then it depends on the target you aim for. Because many just want to double their money in holding it and when they achieve the target they just harvest it. And definitely, most of the holders become greedy when they see the profit is keep rising and many end up with nothing. That's why it is necessary to make a mindset before holding off any asset.
You asked to harvest holding for buying a house, or land, or due to family reasons, which also depends on the emergency and good entry points. Like take an example, you are earning double on your holding and you know, this is not the current time to buy a house/land and there is no family reason but you also knew, that the market will never reach this point again in the next 3 to 4 years and you can not wait for that longer. So, the simplest thing you will do is harvest your profit.
There is another scenario too, in which you knew the house/land rates are decreasing and at the same point you are making the same profit then the answer will be, booking the profit to buy the land so that land could also make you profit because you have bought it at a lower price.
You covered three factors in your post.
Money Management ,
Risk Management , and the third is
Time Management .
This doesn't matter where you are investing. The thing is that how you are investing? Is there greedness interfering? Like you said if anyone has a mind set that he/she will book his/her profit at double of its investment so if he/she will do it same according to its mind set so he/she will get the profit. Otherwise he/she can face losses.
If anyone will understand these three factors which mentioned above and will invest and harvest profit according to these factors so he/she will not face any loss.