From the introduction:
Most of the game of Dungeons and Dragons is focused on the interactions with the things in its name; places of danger and intrigue and creatures that threaten individuals and entire populations. In short; adventures. The many details of life outside this slice of interest are often ignored as much as possible, being less interesting and important as well as far too prone to the fiddly details which turn D&D into Accountants and Actuaries.
Yet, there are always those players who want downtime. The individuals who want to research a new spell, craft a new weapon, set up an inn, tavern, or other business, or otherwise use their hard-won wealth on something other than the adventuring life. Perhaps leaving a mark in the world. Sometimes these periods happen because the DM says so; perhaps they feel the kingdom and world cannot always be at risk and the party cannot always have an immediate lead on a new source of untold wealth and glory. Sometimes downtime is the result of a real world intermission. The days, weeks, and months where real life overtakes players being reflected in the game itself.
For whatever reason downtime happens, this book exists to make it more interesting. These optional rules and options can make the choice between lifestyles mean something more than how much gold is removed from the characters’ pockets. It certainly gives characters, even those “wild souls” who chafe at the idea of inactivity, intriguing choices to make in how they spend their non-adventuring time. For downtime effects, this means adding some risk and reward to the choice of lifestyle. Do you choose the cheaper, but more dangerous route, or the more expensive and safe route? Regardless, life has some inherent risks and on some level all adventurers are looking for their next grand tale.
Meanwhile, downtime actions are about giving characters and players something the character wants that they cannot gain through adventuring alone. Perhaps they simply wish to spend their enforced stillness preparing for their next adventure directly. Alternately, for those who recognize that spellcasters are not the only individuals who need magical items as they progress and question the wisdom of relying on the random detritus lost by their forebears; rules are provided to give the opportunity for noble knights to forge blades of legend. Even the most savage or ignoble members of a party have more intuitive and primal ways to weave of the forces of destiny into enchantments for their equipment.