* To check the sound. Before they start singing, many singers will tap the microphone to make sure that it is working properly and that the sound is clear. This is especially important for live performances, when there is no chance for a retake.
* To create a rhythmic effect. Some singers will tap the microphone as part of their performance, to create a rhythmic effect. This can add energy and excitement to the performance, and it can also help to keep the singer in time with the band.
* To emphasize certain lyrics. Sometimes, singers will tap the microphone to emphasize certain lyrics or words. This can help to add drama or impact to the song.
* To add personality to their performance. Tapping the microphone can also be a way for singers to add personality to their performance. It can show that they are comfortable on stage and that they are enjoying themselves.
* They are nervous. Tapping the microphone can release nervous energy or act as a nervous tic
Of course, not all singers tap the microphone while singing. It is simply a matter of personal preference. Some singers find that it helps them to perform better, while others find that it is distracting.