I had a TA convert a placeholder into a cheap 3 night dummy cruise the day before general public opening day prices. The explanation I got was that she would be able to convert that dummy to the actual cruise we wanted online. If it had remained a placeholder, she would need to wait on hole with DCL on a busy day to do the conversion.
This I understand because I am thinking of not booking placeholders any more and going back to dummy cruise dates so that changes can be done online (also if placeholders are put in my sister's name, I can't get them on my reservation list). But I don't think TAs should be doing it as a general policy and never without telling the client what is happening. Otherwise you end up in a situation like HappilyEverAfter is in. It could be an expensive error if DCL does sail to Hawaii in fall 2018.