There are some HBD Worlds that require their owners to field complete minor-league rosters and keep their players (especially) pitchers from degrading to 0 fatigue. Near as I can tell, these are the arguments against and for such requirements:
1) There aren't enough minor-league players to go around. Technically, this is true or close to it in some of the older worlds (like Belle). It's also true that if all teams signed most of their draft picks and used excess prospect budget $$ at the end of the year to sign int'ls, and paid attention to promote minor leaguers annually (even the ones who aren't prospects), there would be enough minor leaguers.
2) It's too much trouble to manage.
3) It doesn't really matter to the real outcome we're concerned with (major league results).
1) The general argument for the requirement is: "If we want to be a high-quality league, do it the RIGHT way." Don't allow practices that are legal within the HBD framework but are shortcuts that give small but real advantages.
2) In the specific case of minor leagues, the argument is that not signing enough minor leaguers yields a small financial advantage. It's not big - my minors payroll is currently 7.447 mm, and I found one team with 4 mm less. But the question is whether this is the kind of $4mm advantage we want teams to be able to get (as opposed to, say, managing their draft so they sign their picks for $4MM instead of $8MM).
There may be other arguments for or against - post others as replies here or on the World Chat - thanks.