I tried doing the same but found that I could come up with better ideas on my own ironically. I use it when I need a bunch of low quality assets that would otherwise be an afterthought. I was making a card game prototype and I was working solo, so I had no time to really make a different card art for each one..normally I would have had a few redundant placeholder artworks and I would have recycled them for similar cards, or I would have straight up removed the images from the cards, but with Midjourney I could quickly make a bunch of okay images, then I passed them through a few filters to make them appropriate for the game vibe and..that was about it, 2 hours of work and I had something I would have otherwise straight up skipped. But when I asked Midjourney to make anything more specific or important, usually it failed and I went back to manual drawing for stuff like enemies etc.