A passion project is the type of work the creator wants to do and goes against the norms expected by the studio who runs it, aka full creative control, however this doesn't translate to sales or even quality control in some cases, ask yourself if you value having your creation meddled with by your bosses or refusing it and missing out on eating for a few months until the next opportunity arrives.
There are a few case studies to examine.
1. Oban Star Racers
It's gone on record that the creator of cult French anime Oban Star Racers took it personally when the executives wanted the main character to be male, so said creator published the series under his own company out of spite, it found reasonable success but nothing ever lasting, I always believed this to be the closest thing to Star Wars pod racing.
2. Cans Without Labels
John Kricfalusi of Ren and Stimpy fame crowd funded to get his passion project off the ground Cans without Labels, not only was it dreadful, John himself was facing a harrassment lawsuit from a previous employee, it's a great example of the show runner not being the be all and end all.
3. Twinkle Nora Rock Me
Twinkle Nora Rock Me is infamous for being one of the worst anime of all time for the fact that it's creator really didn't know what he was doing, the animation is only a few frames away from being an expensive flipbook, his main reason for making it is, "I just wanted to draw my waifu"
4. Hazbin Hotel
Indie animation tends to be the purest form of creative freedom going and Vivziepop really nailed that with Hazbin Hotel and Helluva Boss, compare that to Wish, Disney's disaster piece which if allowed more freedom could've been a magnum opus but Disney doesn't exactly have the greatest track record of such freedoms, Treasure Planet comes to mind.
5. The Thief and The Cobbler
No animated feature has had as much of a storied history as Thief and the Cobbler, it took from 1964 to 1989 to complete production as much of the issue revolved around finances as it proved to be extremely expensive, it would eventually get a release in 1994 but it was cut and cobbled together multiple times and beaten to the punch by Disney's Aladdin.
11 actors died before it finally got released and in the end, it's creator completely disowned it, a tragic example of how a passion project can spiral out of control.
6. Daicon III and IV
A group of teenage college students created two anime music videos for Nihon SF Taikai, Japan's national sci- fi convention, nicknamed Daicon III and IV as they were held in Osaka for the 3rd and 4th time in 1981 and 1983.
Daicon III features a young girl travelling through the lands encountering various heroes of sci fi and comics, Daicon IV features the same girl grown up in a bunny costume fighting said sci fi heroes including mecha and Darth Vader to name a couple.
In fact it's considered the earliest example of OVA, original video anime, some would even suggest that this is the birth of Otaku and anime as we see it today.
Those teenagers would later become Gainax responsible for some of the most legendary anime ever created.
So what have we learned? It's a mixed bag to be sure but it's a balancing act, think how different the world would be if Spongebob was made a kid instead of a young working adult, if Miraculous Ladybug was allowed to be traditionally animated 2D instead of CGI or if Sandland came out before Dragonball.
For every creator that gambled their house on the success of their show and succeeded (original 90s X-Men)
There's a creator who thinks Christian cartoons was going to rebuild a damaged reputation (Butch Hartman)
It's great to dream but if those dreams start weighing you down and start chipping away at your life then it's better to let them go, success is never guaranteed especially in a fickle industry like animation.
