For me the benefit is knowing without a doubt that this is one thing going on. My symptoms aren't as severe as some; they change; and I have other things that impact my health. Without a diagnosis, I would never be sure and might even think it's all in my head. I have evidence that it's NOT all in my head and I don't have doctors saying, " maybe it's this or that or changing their mind because my symptoms changed or because "I look fine"!-- as so many of us with autoimmune disorders do.
That being said, there can be consequences from having a lip biopsy. When then cut the lip, they cut nerves. Sometimes they regenerate to varying degrees. The numbness in my lip lasted for years and I continue to have some numbness. It's tolerable and I don't notice it too much anymore. I say this not to deter you. I didn't know about this possible result ahead of time and it was quite a shock. Even so, I'm glad I have the result now, as I wade through teasing out other issues.