What's the use of widget id on wxpython?

Question

I've been trying to learn wxpython and I see this id when creating widgets like:

menubar = wx.MenuBar()
file = wx.Menu()
file.Append(-1, 'Quit', 'Quit application')
menubar.Append(file, '&File')

I've read something that says when it is set to -1, its automatically generated but what's the real use of id and how will it be useful to the event?