A singer can overly belt so often and hold the high note so often with a straight, choir-boy light tone that excessive nasality in the voice begins. Using the voice for belting is just fine as long as voice exercises use flexibility and the full extremes of the singer's range BEFORE singing for that day. By using more "tummy" and "side ribs" support and singing on the beginning of the word's vowel formation, the excessive nasality leaves. I had a teenage client who was auditioning for a lead in a high school musical. The nasality in the song was gone by the 4th lesson. The client became the lead in 2016!