Question: Is there any reason why or why not you should do an 'order by' in a subquery?

Answer: 
Unless you use top it is not useful since you will be ordering in the outer query anyway
No ORDER BY is valid in a subquery when you are interested in a subset of the overall data, hence you always need a `TOP` (SQL Server). There's no point having an ORDER BY without TOP in a subquery because the overall ordering of the results is handled by the outer query.