In 1 Cor 14 Paul talks about the difference between public and private tongues, ie Prophecy and 'prayer language'. A prophetic tongue requires interpretation and at the Pentecost event it was those who heard them speaking in their own languages who were the interpreters. But not all tongues in the Bible were so accompanied, nor does Paul ever say they have to be, unless they are public.
What would be the purpose of a tongue, as in the 'prayer language' meaning? Say you are praying for someone, but you don't know everything about their situation. If you knew all the details you could bring them to God, but you don't so you can't. But the Holy Spirit knows them. So if you allow the Holy Spirit to pray thru you, you may 'bring unspeakable things to light'. Likewise, suppose something's going down somewhere and the Holy Spirit needs someone to pray over it. You'd pray over it, if you knew, but how are you going to know? The Holy Spirit knows, and by allowing the Spirit to pray thru us we may intercede in things we know nothing about.
And then there's the origin of 'tongues'. As man's numbers grew after creation he had a single spiritual language. It was one of the few things he kept out of the fall, and it persisted until the tower of Babel (Gen 11:1 – 8). When the Messiah returns to restore all that man has lost, one of those things restored will be that pure singular spiritual language (Zeph 3:9). Christ has won the authority to restore all things, but has yet to return to this world to enforce it. Tongues are a way for us to access that future restored language now, thru the Holy Spirit, so that we may enforce His authority for Him.
Where it talks about tongues 'ceasing' (1 Cor 13:8-10 Love never fails. But where there are prophecies, they will cease; where there are tongues, they will be stilled; where there is knowledge, it will pass away. 9 For we know in part and we prophesy in part, 10 but when completeness comes, what is in part disappears.), it's not that the tongue will stop, but it will cease to be known as a tongue, because it will be instead our native language when Christ returns. At that point English (French German whatever) would be known as the tongue, since they would be the 'outsider' languages. Completeness is yet to come, perfection is yet to come, not in the heavenlies but here on earth. And so the gifts end when Christ returns and bring completeness to us, because at that point they become moot. We won’t need the gift of healing anymore when nobody’s getting sick anymore.
Tongues are not necessary for salvation, nor should it be demanded as proof of Spiritual Baptism. As with all gifts of the Spirit, it is available to all but not required of any... altho God does talk about those who hide their lights under bushels (Mark 4:21, Matt 5:15, Luke 11:33), and bury their talents in the ground (Matt 25:14-28). And the gifts, while not required, are effective in helping produce the fruits of the Spirit that are required. Let me propose that again, the gifts of the Spirit are intended to help us produce the fruits of the Spirit. These include discerningly placed tongues.
Given a good thing, we humans will find some way to screw it up. We will over-use, over-sell, and over-the-top it. That's just our nature. That's when outsiders start thinking we're crazy, and that's where Paul tells some to put a leash on it.
Place and moderation are key to tongues being useful vs being foolish. And being foolish with God’s gifts is never a good idea.
And that includes denying them.
