Good quality machines are accurate & precise. If instruction given in sugar testing machine followed properly there should not be any problem. As there are many differences in the methods of testing (e.g. machines uses capillary whole blood & estimate blood glucose whereas laboratory uses venous blood for plasma glucose estimation), one should not compare accuracy & efficacy of machines with laboratory.
Machine detects ups & downs of blood sugars at an early stage. It is the only way to know how the body responds to changes in diet, exercise, tablets & insulin and will help in adjusting the therapy to achieve specific blood sugar goals. It is the only method of diagnosing hypoglycemia (low sugar) at the precise time of its occurrence. It will also help in identifying insulin doses during intercurrent illness.
It is important to know that good machines still have a margin of error of at least 10%. Precision & accuracy of machines need to be assessed periodically to guarantee the quality of data with quality - control solution. Laboratory testing is good for finer control.