One of the things I am is a Medievalist, which is probably why I like Fantasy Roleplaying Games (they’re usually at least “pseudo-medieval”). And one of the interesting things about the Middle Ages is their attitudes to what we would call “authorship”.
In our era, the “author” of a text is the person who made it up out of their own knowledge and imagination. But that was only one of four Medieval ways of “making a book”.
If you composed an original work based on your own ideas, using your own words, you were an auctor (the Medieval Latin root of our word “author”).
But perhaps you were just the person who transcribed the words (the auctor may not have bothered to write their composition down, and certainly wouldn’t have made every copy of it). Then you were the scriptor, or “scribe”. And before you dismiss these folks, know that Medieval scribes regularly made a lot of “helpful corrections” to the texts they copied, sometimes considerably altering the meaning of the work in the process.
Because Medieval scholars valued works from the past (especially religious writings), their work often consisted of writing interpretative commentaries on these works. In which case you were a commentator.
And finally, if you pieced a number of related works into one larger work, you were a compilator, or “compiler”, and this is the kind of author that best sums up the Homebrew Gamemaster.
Building and running an entire world is a big ask. Most people just can’t do it alone. Sure, there are famous exceptions: Tolkien’s Middle Earth; Ed Greenwood’s Forgotten Realms, George R. R. Martin’s Westeros. You know what these authors have in common? They are (or were) hella old men who had decades to work on their fantasy worlds. And even so, if you scratch the surface, you’ll find they were compilers too. The basis of Tolkien’s work was language, and his elf languages were derived from Finnish (for Quenya) and Welsh (for Sindarin). He took the dwarf names from Old Norse. And if you’ve read Medieval literature or studied Medieval history, you’ll know where George R. R. Martin drew much of his inspiration.
But there’s an even better reason to be compiler than merely decreasing your workload, and that’s the sheer bulk of amazing material that already exists out there.
As a case in point, I dislike High Fantasy, High Magic settings, so I’ve never been interested in most of the official adventures for Dungeons & Dragons Fifth Edition. But I love Gothic Horror, and I was already a fan of the original Ravenloft module, so I bought a copy of Curse of Strahd and decided that Barovia would be a part of my world. To stop it jarring completely with the Early Middle Ages feel of my starting area, I put it on the far side of a divisive mountain range, reachable only through a dangerous mountain pass called the Bjorgir Pass (inspired by the Borgo Pass, as mentioned in Dracula), which is full of monsters. The adventure hook is that the creatures who live in that pass have been venturing out, into the Northern part of the world, and some adventurers are needed to investigate it (as detailed in my post on running Curse of Strahd for my kids). Of course, when they do, they get trapped in Barovia by the mists and have to remain until they defeat Strahd.
The upshot of this is that, if my players are successful, they will effectively open the Bjorgir pass for trade, creating a direct link through the mountains to the mysterious east. So by importing someone else’s material into my setting, I got a fully fleshed-out adventure region, a compelling adventure quest, with any number of side quests, and a long-term consequence for the world as a whole. All because I think vampires are cool.
I have also found places in my world for Chult, the Temple of the Frog, the Tomb of Horrors, and Rappan Athuk. And this is in addition to the homebrew areas and adventures I have created from scratch. So my world is really a pastiche of things I’ve made myself, supplemented with my favourite material from D&D’s past and present. It saves me work and gives my players a chance to experience some of the classic modules, like the Temple of Elemental Evil or the Keep on the Borderlands (neither of which I’ve used yet, but definitely plan to).
The reason to start homebrewing is because you have your own ideas. But others have good ideas too, and if you like them, use them. Sew them into your own world. You’ll only be making it richer.