This feature allows you to load more than one log into the same tab so that it's easy to compare repetitions of the same game scenes, with changes between runs.
To use it, drag more than one log at the same time onto the tool. One log will be the base one (named in the tab) and the others will be sub-entries in the Overview hierarchy.
For example, here's the Forest level timedemo run, with & without GI enabled. To make it easier to read I filtered the list down to 1 information track (numTotalDrawCalls).
Lining up the 2 logs
In the top right corner above the tabs for overview, function profile etc... it displays which logs are active on the display. You can enable / disable them by un-ticking the checkbox.
The colors are also defined here for the different logs. (Rnd = random color button).
Also available are the number spinners for each log. The first one is for the starting point (0 & 0) and the 2nd is the final frame in the log (8576 & 8533).
In the top picture I used Start SinglePlayer/Forest SinglePlayer), as the reference point.
With my reference point chosen, use the spinners to shift one log or the other left or right to make the same ref point on each track line up.
Alternatively, in the User markers tab you can right click on a user marker & set the start / end frame there.
Although not a perfect system due to slight changes between runs, (longer loading times etc...) this helps view the 2 logs when overlayed on each other.
So by using this system, you can make it a lot easier to read the 2 charts compared together.
After - Much easier to read.