(The following is something that came to mind while I was methodically watermarking my images one day).
My watermarks aren't really designed to prevent theft. Because even though I could make it more frustrating for thieves to steal my work, there's a tradeoff point at which it starts to detract from the art. And let's be honest, if a thief is determined enough, he'll find a way. I don't condone it, but I'm not gonna wring my hands and let it ruin my enjoyment of sharing the art I create. Plus, I don't just produce images, I consume them too, so I know what it's like to be on the other side of the screen, and I know how the photo sharing community operates. I don't position myself in opposition to a community I identify with, and I'm not out to condemn perfectly reasonable fair use applications of my work, because I don't want to be a hypocrite.
The reason I use watermarks is partly to claim my copyright in an official capacity, but mostly as a tool to aid the relationship between art and audience - so that people who see my work will know who made it, and will be able to seek out more like it. Yes, it helps me by establishing my brand and serving as a low-key form of advertising, but it's also for the benefit of fans. I don't want to be obnoxious or pretentious, so I try to maintain the right balance, but I do also respect the value of copyright, and the importance of an artist to confidently claim ownership of their work. That's why I continue to watermark my images, even though it increases my workload, and can be a real pain in the ass sometimes.
When I'm deciding how to put watermarks on my images, I approach the process primarily from a perspective of good faith, and not with the intention to deter bad actors. Some might call me idealistic and naive, but I prefer to think of it in terms of positivity and kindness. Because if you're not respecting my copyright (and really, I'm quite lenient, as long as you follow common sense - my main concern is other people taking credit for my work, as well as any money that should rightfully be going into my pocket), then you're not respecting me. And if you like the art I produce, then why would you disrespect the person who produced it? We are all vulnerable to exploitation in this world. My goal is to spread happiness and joy, while counting on being someone that I would hope people would not WANT to exploit. And it may simply be because I'm just not that popular, but so far, it has worked for me.