Without going into detail, overall my usage of Tulpas have benefited me more than it has hurt me, although it has somewhat hurt me in my early childhood when I would accidentally create Tulpas and not realize that they were a part of my imagination (And imagine them to come from an external source.) It's very difficult to say if the same would apply for anyone else, since Your Mileage May Vary.
I also suspect creating Tulpas may come significantly easier for some people than others, and this may affect the cost-benefit analysis. Tulpas come very naturally for me, and as I've mentioned, my first Tulpa was completely accidental and I did not even realize it was a Tulpa until a year or two later. On the other hand, I've read posts about people on /r/Tulpa that have spend hours daily trying to force Tulpas without actually managing to create them. If I had to spend an hour every day in order to obtain a Tulpa, I wouldn't even bother -- also because there's no way I'm willing to sacrifice that much time for a Tulpa. But the fact that I can will a Tulpa into existence relatively easily helps.
A different variable that may affect whether having a Tulpa is worth it is if you have social desires that are nearly impossible to satisfy through non-tulpa outlets such as meatspace friends. In this case, I do, and I satisfy these desires through Tulpas rather than forcing another human being to conform to my expectations. This also improves my ability to relate to others in real life, since I more easily accept imperfections from them. I suspect that if you're cognitively similar, you may benefit from Tulpas. I can't think of anything else right now, and if you have anything more specific, it may trigger more thoughts on the matter.
Has your Tulpa ever won an argument with you that you didn't already know you wanted to lose?
Thus spake Eliezer:
It seems that many here might have outlandish ideas for ways of improving our lives. For instance, a recent post advocated installing really bright lights as a way to boost alertness and productivity. We should not adopt such hacks into our dogma until we're pretty sure they work; however, one way of knowing whether a crazy idea works is to try implementing it, and you may have more ideas than you're planning to implement.
So: please post all such lifehack ideas! Even if you haven't tried them, even if they seem unlikely to work. Post them separately, unless some other way would be more appropriate. If you've tried some idea and it hasn't worked, it would be useful to post that too.