This trains the ear to know intervals. It trains the voice to sing the exact pitch by “jumping intervals” practice.
Examples:
Root note always first, then 4 5 4 then root always last [sub dominant, dominant]
Root note then 3 5 3 then Root note always last [chord]
Root note then 3, 3 flat, 3 then root again [minor]
Make up your own sequence comprising of eight notes. First play the root note, then 3 notes that are in the upper part of the scale, then 3 notes in the lower part of the scale, then the root note again as the final note. Practice the custom sequence in every key.
Always the root first, then the sequence, then the root as the last note. Mentally think and feel the note positions in the scale as you vocalize them.