Obviously each team in both Munster and Leinster will have one “free” weekend off when there are two other matches taking place in the same province.
Are these matches going to be played over five consecutive weekends so? Presumably they are. Order of fixtures could be important so, you’d prefer to play two weeks in a row, a week off, play two weekends in a row rather than being idle the first or last week and playing four weeks on the trot as a result.
Also the team not playing in the last week may be at a disadvantage as the other four teams in action will know exactly what result they need (i.e a team might know they’ll have to win by four points or more to progress on scoring difference)