First of all, I believe in speaking in tongues as one of the gifts apostle Paul mentioned. I DO speak in tongues and I do discern what I speak. I DO also sometimes discern what people speak. But there's this trend even among pastors that speak in tongues without interpretation. How would the congregation understand? Paul who emphasized on tongues clearly also says that it's better to speak few words of understanding than ten thousand tongues.
Note: I know some believers don't agree with tongues but I do agree but not speaking without interpretation.