Park Pass Reservations

I am scheduled to travel to WDW in March for 4 days. Do any parks actually close to capacity besides HS? I read somewhere to reserve passes for HS for multiple days to give ourselves multiple chances to get ROTR boarding groups. For example, try on day 1 at 7am and if you miss getting a boarding group to switch the park pass to a different park for that day, and then try again day 2. Ultimately I would like to visit each park one day. Does this make sense? Am I in danger of not getting a park pass for a park if I need to switch at 7am? Thank you

I have heard that it has been fairly easy to get into the parks recently.