Thanks for posting. You'll note that I moved your post. It is ABOUT exercise journals, but it is not a journal, so I took it out of the journal forum.
A word of caution. If you are here to sell your app, you will disappear faster than a candy bar at a WWA meeting--we don't allow the promotion of commercial products. But if you're here to discuss the topic and methods of journalling, and maybe even participate in other discussions as well, welcome! And thanks for being up-front about your app.
I journal on paper most of the time, but transfer it to an on-line journal (not surprisingly, I use this forum to journal). I track the workouts in order to document my progress or lack thereof, to try to sort out what exercises and what routines are more effective for me, and as a reference workout-to-workout for the loading and rep scheme for each day. Doing it on the forum allows my cyber friends to comment, make suggestions, give me praise for my amazing progress, etc. My present phone is not smart (though this may change soon), so that option is out for me for the moment.
Our greatest fear should not be of failure, but of succeeding at things in life that don't really matter.--Francis Chan