Personally I think it's a great idea. I run my own instance even though I'm the only user and have no communities.
Pros:
Moderation: Your own moderation capabilities. It's your choice what you see or don't see.
Content longevity: You can do your own backups and don't have to worry about loosing content when another instance disappears.
Performance: Generally speaking you'll have better performance. You won't have to worry about an influx of new users taking the instance down due to overloads.
Cons:
Domain: You need your own domain, which is an ongoing cost.
Hosting: Like the domain, you need to pay for hosting to run Lemmy. You could try running it at home, but I would not recommend it.
Management: Depending on how you setup Lemmy, there will probably be ongoing maintenance work. It might not be worth the hassle when you can just use a third party instance and let them deal with it.
Ultimately it's up to you.