The log readers are separate stand alone programs that run
along side the game. The game must be started first, including all
instances you plan to run, before starting the log viewer.
Once your enable logging, all the content from your chat window(s)
gets written to a text file i.e..
nwn/logs/nwclientLog1.txt.
I dont know if the other log viewer HGX has a way to force the game
to create instancelogs but for me, every instance writes their logs
to the same file.
This means that sometimes the logs get stepped on by the different
instances of the game, and whacks up its content. Basically making
the file unintelligible to the log reader.
All the content you see in your chat windows including battle content is saved
to those log files. The log reader filters, collates this data, and
displays it into logical groups for ease of reading. This lets you see things
like fugue timers, how much damage you are taking and dealing, and what
types of damage it is. Saving throws, spells, GS timers, basically any thing
that shows in your windows can be organized for viewing.
This is how you are able to see how much damage you totalled for an entire run,
how many kills and deaths you, and your party members had etc....
Do note, party members must be in range of you to track their info.
Basically if you are far enough away from the battle to rest, then
none of the combat data is making it to your logs. At such times
only your info will be tracked in your logger.
In a nutshell, I find the most useful aspect of a log viewer to be:
tracking fugue timers
seeing what type of damage I am taking, so I know what immunities I need to cover
seeing types of damage I deal to enemies, to know what damage types I need to focus on
seeing how my stats compared to the rest of the party, to know if I pulled my weight or not
Hope this helps
Cheers