Check out HEM's website for more detailed info - better yet, download HEM, a free trial for LB is part of the overall HEM trial. The LB trial does not include all the functionality, however (for obvious reasons).
In a nutshell, LB compares your statistics against "optimal" players, where "optimal" is defined as what winning players are doing. There are a large number of data point comparisons, from basic stuff like VPIP/PFR/3bet etc. to some detailed stuff by position etc.
LB also provides a number of suggested strategies surrounding a variety of topics, and includes a number of filters that you can use to check your performance in HEM against specific types of situations.
It's time consuming because, if you're like most players, LB will identify several potential/actual leaks, and understanding how to resolve/address those takes a lot of study. Fixing one leak may produce another problem (oooh, I'm not 3betting enough, I better start - oops, I'm losing money when I 3bet, what am I doing wrong???), since your play as a whole is impacted when you change something dramatically.
edit: When I was considering buying the module, absoluthamm recommended I not do so unless I was willing to commit the time. I completely agree w him and make the same recommendation to anyone else.