The minimum plot size is k=32. There is only one reason why you might want to plot larger than k=32: to maximize the total utilization of a given drive or space. A couple of k=33 plots with a majority of k=32 plots can reduce the amount of leftover unused space on a drive.
The reason k=32 was chosen as the minimum plot size was to prevent a short-range replotting attack, which is detailed in our consensus doc. The gist of the attack is that if someone can create a plot in less than ~30 seconds, they could create a new plot that passes the filter for each signage point, and then delete the new plot immediately afterward. This would effectively emulate storing 512 plots, thus turning Chia into PoW.
- Note that this attack does not create a winning plot; it only creates a plot that passes the filter.
This attack won't be economically feasible for some time, if ever. Two potential mitigation techniques are to lower the plot filter (thus reducing the benefit of the attack), or to increase the minimum plot size (thus making the attack more difficult to perform).
k=32 is expected to be the minimum plot size until at least 2026. If and when that size is increased, you will be given ample notice to replot before the change is made effective.