Simply said, ketones are the "ash" of burnt fat cells. If weight is coming off fat cells are burning and ketones will be present, this is ketosis. Some people spend money on strips to check their urine to see if their body is in ketosis, I simply watch the scale...if the weight is dropping fat cells are burning.
In the long haul, the scale alone will tell us if fat is burning.
However, for those of us who
lose weight very slowly (like me) and/or don't see much change in the scale over periods of time, these strips are helpful in verifying that ketosis is still happening even when the scale is "silent".
I use them when I don't see
weight loss on the scale for two (or more) weeks or, when I suspect that I might have eaten something high-carb that stopped my
weight loss.
They are inexpensive and seem to help my morale at those times when I think the scale should be moving down, but isn't.
They are also more convenient than taking frequent body measurements.
This is just my personal preference.