How does the localisation mode in slam toolbox work?

edit

I am kind of new to slam_toolbox. I have used gmapping + amcl in the past.

I request someone to confirm my understanding of the localization mode and correct me if it is wrong. I am using the melodic branch btw.

So first of all, I create a map using either the online async or the online sync launch file, and then at the end I click on the serialize map button on the rviz plugin which creates the abc.data and abc.posegraph files in ~/.ros. The mapping part worked beautifully.

Now if I want to localize on the map that was created (similar to what AMCL does), I would use the localization launch with the 'localization' mode, the file name, and the start pose specified in the localization YAML file. This should basically help the robot localize on the map that was created earlier.

But when I tested this, it does not seem to work like AMCL. The map still grows (it looks I am still mapping).

Thanks in advance.