People go a little crazy about impellers. It really depends on the types of lakes you run the boat in when talking about when to change it. If you fish the kawarthas you need to be changing that thing regularly. If you mainly fish open water on the shield Lakes you can definitely push replacement intervals out a little longer. The rubber does degrade over time so eventually they need to be changed, but in general if you are fishing clear rocky lakes and not running your motor through the junk, rice, grass, slop and mud like on the kawarthas all of the time you should be good to go.