This module will prune the chat log so that not as many chat messages are rendered in it at once. This improves performance, as a giant chat log (it gets big!) is one of the prime causes of a laggy foundry app.
It does not delete the messages.
You can scroll back and see them, just like normal. When you get to the top of the chat scroll bar, there is brief pause while old messages are rendered, and then you can scroll up more.
Upon scrolling down to the bottom, the extra messages are removed. They are also continuously removed as new ones are added during play. This way the rendered log never gets that big, even after several combats.
But again, the messages are not deleted, this just limits how many messages are in the chat log scrolling window at one time during normal use.
The settings for the module allows the number of messages kept rendered in the log to be configured. The Foundry default is 100. And the number rendered in each batch when the log is scrolled to the top can be changed too.
This module drops the initial number of rendered messages to 50, making the client start with a chat log half the size (assuming you have 100+ messages in the history). If you find the pause when old messages rendered into the log annoying, setting this back to 100 will mean you can scroll back the same amount as stock foundry without a pause.