From the introduction:
In a typical campaign, it’s possible for the characters to start at 1st level, dive into an epic story, and reach 10th level and beyond in a short amount of time. While that pace works fine for many campaigns, some DMs prefer a campaign with pauses built into it—times when adventurers do things other than go on adventures.
By introducing downtime activities that take weeks, months, or even years of effort, you can give your campaign a longer timeline that allows events in the world to play out over the course of years. Wars begin and end, tyrants come and go, and royal lines rise and fall over the course of an entire lifetime of adventure.
The downtime rules also provide ways for characters to spend the monetary treasure they
amass on their adventures.
The options given here can be used as alternatives to the downtime options in the Player’s Handbook and Dungeon Master’s Guide, or you can use the material here to inspire your creation of new options.