It only makes sense from an entertainment profession standpoint to have eyes and ears in as many social circles as possible adjacent to your field so that you can keep track of gossip and news regarding you, your agency, your co-workers, etc. That way you can observe live reaction and fallout to your actions and see what works best for certain demographics and what turns them away. Can be useful if you have a certain audience you don't have an interest in either because of ideological differences or just behavioural issues, but also handy to know any harmful rumours that are circulating so you can attempt to get ahead of them, quash them or otherwise do something about them and set some rrat poison to stop the spread.
Whether the talents themselves do it, or there's staff on hand from the companies themselves that act as intelligence agents to watch the spaces and report back broad strokes information and the occasional live rrat, always presume that any publicly accessible social site may be under observation and that you and your posts may be taken as a metric of measuring success. Your oshi may be watching, or they might hear about some weirdo thirstposting over them second hand. Question is, are you going to let the fear of being observed prevent you from loving your oshi? Or are you double to redouble your efforts so they can see how true and honest your feelings are so they know who their strongest soldier is?