Most people are under the impression that the only time you need to sage your home is when there is spirit activity. That is not true. There are many different reasons to sage your home. One would be if you have had an increase in the number of people entering your home. Whether it is family or friends everyone carries energy with them. If there has been a lot of "going in and out"much of that energy can get left behind and builds up. After a while you can actually feel the thickness in the air.
Another reason would be after an illness.Just like you would disinfect doorknobs etc. it is good practice to crack the windows and whisk the leftover gunk out the door.
Last but not least if you have anyone who resides in your home who has an addiction,mental issues or is just plain old negative it is a good idea to sage regularly. Again you just don't want that stuff hanging around.
Other than the reasons just mentioned you should always sage when you are moving out of a place(you don't want anything coming with your things)so as to not leave your energy behind and of course sage wherever you are moving to before you move in,especially if you are planning on doing any renovating.So in conclusion always have that sage stick stocked and ready to burn ! Blessings!