If you have a handbook that has content that only applies to specific subsets of your audience, groups are going to be important. Groups, in short, are the marker that makes the employee user experience better. When sorted into groups properly, Org Members only seeing material in the handbook that is relevant to them.
For example, if you have employees in different states and you only want California folks to see California policies, you'll want to create a state Group. If you have managers and contractors that have different policies you'll want those job titles as Groups too. This is no limit on the amount of groups you have or what you label them; however, best practice is to only create the groups you'll actually need.
Want to see how you set that all up? You can read more on how to set up these groups here!