You said this in context with how you would have rather had someone with the gift of healing visit you, while you had cancer, rather than someone speaking what you could not understand. I offer that I understand this point you are making. And I am sure our Apostle Paul agrees with you
About if speaking in an unknown language can be useful. If the Holy Spirit has someone do something, it is useful . . . whether people understand what God is doing or saying, or not. I think a number of us have done things with God, but we did not understand at the time what we were doing. So, whether we understand actions or words is not necessarily relevant, I consider.
But our Apostle Paul does say it is better if a tongue speaking is interpreted, of course. But even if someone is simply praying in another language and no one gets the words, still the Holy Spirit can be ministering grace deeper than words >
"As each one has received a gift, minister it to one another, as good stewards of the manifold grace of God." (1 Peter 4:10)
True speaking in tongues is a gift; it does minister God's own grace. My opinion is there can be times when tongue speaking is not meant to be interpreted, but it is a prayer thing. And Paul does talk about how it can be praying well. And prayer does minister God's grace, even to ones not present with the praying person. So, we do not have to hear and understand what a person is praying for us.
But I understand that there can be faked speaking in tongues. I do not believe it is possible to control a gift of the Holy Spirit to do things in a wrong way. On the other hand, it seems there are people who simply don't buy tongues and so they will find ways to criticize it and misrepresent it and argue against what isn't even what the Bible says about tongues.
Why would people have such a problem with any sort of real speaking in tongues? Because humans are antagonistic against being submissive to God. And tongues . . . real tongues . . . is the Holy Spirit having a human speak a language the human does not even know. So, this takes submissiveness to the Holy Spirit, in every detail of what the Holy Spirit has the person saying. And ones do not want this, their spirit is against this. And the grace of this can change us so we more and more submit in every detail in all we do, because the Holy Spirit having one so speak can also have the person more and more submitting to all else which the Holy Spirit has us doing. This could be part of why Paul says someone speaking to oneself edifies one's own self. But others in spiritual connection with this can also deeply so benefit, though they are not having an interpretation.