I bought the vacuum because it was advertised as only needing to be emptied every 30 days. It wasn't until I bought it that I found out that they recommend cleaning the filter every week. My robot "Alfred" is set to automatically clean for several days in a row. I couldn't imagine having to wash and deactivate the filter while waiting for the filter to dry. So I decided to buy an extra filter. I take out a filter and put in a spare. That way I don't have any lags and I don't have to worry about the filter not drying out after washing.