Were you better at the exercises of this week or the previous? How many words are you confident that you learned? Tracking your progress motivates you to learn.
When you are learning something it is really important for you to know how you are doing on it. That helps you to know what you should improve and how to do it, that what tests are made for.
If you have a goal and track your progress that motivates you to achieve it. This avoids you to drop out from study a foreigner language, which tends to take some time before you get comfortable with it.
Self-Polyglot helps you to monitor your progress checking how many answers you did right and wrong and on each, you are doing every day.