Within your LMS it is vital that you measure the usage through reports. There are many reports that could be created to track activity but some are vital to ensure you get the most from your LMS.
Hits - Measuring how many hits on your site and content help you see which content is most popular. If a certain type of content gets more hits than others it will help in the production of future content.
Completion - If a user has accessed a piece of content it doesn't mean they have completed it. Completion reports allow administrators and managers to track completion of content and when users have completed them.
Analytics - Using the Google Analytics API there are a variety of metrics that can be tracked such as Device Type, Access Time and Geographical Location. These can help to tailor content to audiences and, if you have multiple locations in your business, see which locations access the system.
The above are just a few general reports that are useful within an LMS, however depending on the system you may want to go deeper by reporting on how users interact with certain content, such as the answers they give to quiz questions or the progress they make on certain SCORM packages.
When choosing your LMS it is vital that reports aren't an afterthought and you are tracking what is important to your team and organisation.