Yes. You can safely add it. The plugin won't modify any existing entries in the log table of the Elgg database. It will just stop new entries from getting created (and if you would disable the plugin again the log entries would start to be created again). If you have the logrotate plugin enabled and the Elgg cronjob added on the server for the intervals set in the lograte plugin settings for rotation of the log (archiving) and deletion of archived log tables the already existing entries in the log table will automatically vanish after some time resulting in the log table getting smaller (in the best case 0 entries in the long run). Of course, without entries in the log table the logbrowser plugin of Elgg won't be able to show any entries anymore. But these log entries are mostly of no use anyway.
Hello. Can I use this plugin on the existing website with huge content safely?
Yes. You can safely add it. The plugin won't modify any existing entries in the log table of the Elgg database. It will just stop new entries from getting created (and if you would disable the plugin again the log entries would start to be created again). If you have the logrotate plugin enabled and the Elgg cronjob added on the server for the intervals set in the lograte plugin settings for rotation of the log (archiving) and deletion of archived log tables the already existing entries in the log table will automatically vanish after some time resulting in the log table getting smaller (in the best case 0 entries in the long run). Of course, without entries in the log table the logbrowser plugin of Elgg won't be able to show any entries anymore. But these log entries are mostly of no use anyway.
Thank you for the clarification.