I currently use a monthly planner and also a weekly planner. I know there are some people who find that using both renders one of them obsolete but I find it so handy to have both. I use my monthly planner to write down plans that are happening well into the future and to keep track of birthdays and special dates. I also get my work hours for the month so it's nice to have them written down in one place where I can just look at it in one go. Hence why it's called month at a glance!
I almost never write anything directly on the page. There's this wonderful thing called washi tape and it's re-positionable so if a plan changes I can just lift it up and move it to where it needs to be. If a shift at work gets changed, I can just peel it off, chuck it in the bin and write a new one. It's so much nicer than crossing things out or using correction tape. It makes my heart happy because everything looks so much neater.