sudo pacman -Syu is equivalent to sudo apt-get update && sudo apt-get upgrade, you'd want to run it about once a day to ensure you have all current updates. Pamac should allow you to update everything from a GUI, so you don't have to worry about that.
Packages get updated a lot in arch. Occasionally a package may push an update with a big that can cause major problems. Often times those bugs are fixed relatively quickly, but if you update too often, you are more likely to update to a package with such bugs.