Be not rash with your mouth, and let not your heart be hasty to utter any thing before God: for God is in heaven, and you on earth: therefore let your words be few.
Sometimes people feel they're doing God a disservice for not being in prayer long enough, as if the Lord is our lonely granddad and we're such ungrateful sprogs that picking up the phone to tell him how we're doing is beneath us. People often say you gotta be “in prayer,” or be a prayer warrior (and I'm not meaning to discourage people from doing anything in prayer). Still there are examples in the scriptures of a bad prayer life, an unhealthy history of communication with God. Christ rubber stamps King Solomon's wisdom in the above verse when He teaches (Matthew 6:7):
But when ye pray, use not vain repetitions, as the heathen do: for they think that they shall be heard for their much speaking.
“vain repetition” is translated from the Greek “battalogein,” which is a sort of mystery word to us today, not being used in the contemporary literature (although several credible theories are attached to the origins of the word), “for their much speaking” makes total sense nonetheless. To speak much and think highly of assailing or befriending God by many words is against Solomon's view in Ecclesiastes and Christ's view in the New Testament. Jesus taught a similar skin on bones simpleness around the topic of swearing oaths (Matthew 5:37):
But let your word ‘Yes’ be ‘Yes,’ and your ‘No,’ ‘No.’ For whatever is more than these is from the evil one.
The lady doth protest too much is the modern day equivalent to overcooking an oath, an action which Jesus teaches is an evil thing. These kinds overextension of our oaths and prayers are in the opinion of Solomon more likely to harm our relationship with God than anything else. They're not likely to belong to a petition He's open to hearing. Being clear though these verses aren't against repeating a request in prayer, as Christ's parable of the persistent widow teaches to be in prayer and not be discouraged (Luke 18:1-7):
And he spake a parable unto them to this end, that men ought always to pray, and not to faint; Saying, There was in a city a judge, which feared not God, neither regarded man:
And there was a widow in that city; and she came unto him, saying, Avenge me of mine adversary.
And he would not for a while: but afterward he said within himself, Though I fear not God, nor regard man;
Yet because this widow troubleth me, I will avenge her, lest by her continual coming she weary me.
And the Lord said, Hear what the unjust judge saith.
And shall not God avenge his own elect, which cry day and night unto him, though he bear long with them?
So Jesus and king Solomon don't appear to be against repeating requests in prayer, and God who gives everything is prepared to listen and provide for our needs in these things. “God is in heaven, and you on earth,” Solomon teaches, meaning God's in an exalted position and in authority over us. Furthermore, in light of Christ's unjust judge, God (who is just) is able to accomplish those needs of ours, but that's done on His terms and in His time as a result of our faithful petitioning. These petitions being conditioned on our faith is drawn from how Jesus bookends the parable (Luke 18:7-8):
And shall not God avenge his own elect, which cry day and night unto him, though he bear long with them? I tell you that he will avenge them speedily. Nevertheless when the Son of man cometh, shall he find faith on the earth?
So what kinds of prayer to the Lord are considered unhealthy. Solomon wrote against a hasty, thoughtless prayer life, whereas Christ taught against repetitious rotary style prayer which is a kind of time sink and false piety.