The data will be consistent, even if it is not always accurate, so your activity will be compared day to day.  The reality is most people do not realize how little they actually move - these devices can be great to bring that to light.  Gee... I've only taken 3,000 steps today - do I sit to watch TV this evening or get out for a walk or tennis/squash game?  That's the value.    If you're leaning towards obsessive tracking, well this is only one tool and may not be helpful.