I use Arccos and have been using it for 2 years. It has been terrific. In a round, it has helped in club selection based on both historical yardages for specific clubs and current conditions on the course. Additionally, I use it much like a range finder to query distances to various positions on the course hole and visualize specific shots.
Off the course, I use the Arccos application to review my club distances and re-evaluate gapping of my clubs. Also, using the application, I review the course to familiarize myself to each hole and develop a plan to attack the course.