You should clean your diffuser briefly every time you change oils and between uses. You should perform a deep cleaning on your diffuser once a month to ensure that there is no debris and to prevent any blockages.
If you invest time into cleaning your diffuser, it will perform better. If you don't, it will not function at its peak capacity, and you run the risk of accidentally mixing aromas. If your diffuser comes with a cleaning manual, this should be followed. If there is no manual, you can use the advice you find online.