Actually, if you are planning to go to DL and go immediately on rides, particularly in Fantasyland or Tomorrowland (since the monorail leaves you in the middle of Tomorrowland), by using the monorail you can save a lot of time not having to go to the front of the park, going through long lines, and heading back to those areas . . . it also gives you a great view as you go past CA park. However, you are right in that the monorail isn't crucial as it is at WDW. You can get around perfectly fine on foot.
How does that work at park opening time? We figure we'll be there at opening each day because we'll still be on East Coast time, and I would want to be at an entrance where we can get into the park as soon as it opens.