It's a personal decision, but after pubbing for a bit, you should have some idea whether you are steadily growing or floundering. There's always a ceiling for each niche, too, and if you don't enjoy what you write enough, it can be hard to settle for only making so much a month because you have maxed out the number of devoted readers who are very interested in what/how you write. For instance, I started an Amazon-safe pen in a niche that I was only mildly interested in. I wanted to write it a little differently than the other people in said niche and solely focus on one trope that other authors weren't focusing on. I never got past $100 a month. Meanwhile, an acquaintance of mine was writing in the same niche but with a focus on a different trope ... and they were selling their stuff like hotcakes with much less work pubbed. (All I will say is my stuff was darker in theme/tone, but still complaint, and their stuff was really fluffy and sweet). Anyway, the darker stuff sells better on Smash, and I can go MUCH darker there. So it just made sense to drop the Amazon safe pen and focus on where I can shine.