Edge plating/castellations/milling (not drilling) copper in general is one of the biggest causes of scrapped boards in the PCB manufacturing process as the the lateral movement of the drill bit causes the copper layer to delaminate. Most board houses will upcharge for this because all of the problems it causes.

Improving PCB manufacturing yield is a very complex discussion which the concept of aesthetics has actually been a major problem in the industry since the 80's when operators would endlessly reflow solder joints until 'they looked good'.

While the rest of the advice is not bad, there are objective reasons why it is better that way other than the subjective reason of aesthetics.

I believe the only castellation is the large half-hole for mounting.