I use them when i introduce a new food. i check to see if that food has knocked me out of ketosis. i think they are great for people to use in the beginning, but after you have been doing it for awhile, i think most people get to know their bodies. i am not that far yet! i just recently found out that the atkins candy was knocking me out. none of the other lc candies had that affect and i didn't even test after the atkins ones until i had ate about 4 of them over a 2 week period and hadn't lost anything. i could have saved myself 2 weeks by testing when i first tried those bars.