This is a very valuable question to ask, because let us remember that the majority of productions of this play cut this section of this scene, finding it too different from the tragic events that have just occurred with the discovery of Juliet dead (supposedly) on her wedding day. Certainly the humour and insults that characterise this scene seem rather incongruous given the tragic nature of the rest of the scene. However, it is possible to view it as a kind of a release of the tragic tension of what has just happened and what is about to happen in Act V. It can therefore be argued that this scene provides us as an audience with a bit of a space to breathe and helps prevent us being overwhelmed by the tragedy of this play.
In addition, if we consider how servants are used in this play, we see that servants provide a different take or view of what is going on in this play. Here, the musicians present a rather different perspective of the working classes to Juliet's death. Initially, they refuse to play a cheery tune because of their fear of getting into trouble with their superiors. However, as the scene progresses, it is clear that they care nothing for Juliet or her tragedy. They are far more concerned by the fact that her death might rob them of a free lunch. Through this scene, therefore, Shakespeare gently reminds us that the tragedy of this play is not actually a tragedy to everyone. Perhaps we can thus see this scene as providing us with some perspective on the otherwise overwhelming events in this tragic play.