GOING TOO SLOW — The most obvious problem with going to slow for singers or wind instruments is SUSTAINING A LONG HELD NOTE or carry over a PHRASE. The next most obvious problem is the tendency to go FLAT, or LOSE PITCH. The right TEMPO usually helps with being able to sustain pitches and stay in tune.
I once saw a piece marked on purpose “Excruciatingly Slow.” Hopefully that piece was to be played by a keyboard or strings that do not have breathing issues. It is painful just thinking about it!
PRACTICAL EXAMPLES: In Primary, unfortunately, some accompanists do not have much training or skill. There always seems to be the lady that can play just in one TEMPO. And whether that TEMPO is FAST or SLOW, it is still not right for every song.
Singing a song like “I’m Trying to Be Like Jesus” too quickly turns it into a galloping horse-ride and doesn’t maintain a reverent attitude. Singing “Love One Another” too slowly makes it sound like a funeral dirge and the long phrases become impossible to sing.
The proper TEMPO really does matter. Always try to practice at the METRONOME MARKING. Composers really do try to think through what would be best for their pieces.