Hello Annapurna,
If I understand your question correctly, you're asking what you gain and/or lose with a live connection (a DirectQuery)? Is that correct?
Assuming that's correct, there are several links that provide much more detail than can be provided here but in general a DirectQuery is designed for large data sets and some of the standard functionality has been disabled to prevent your dashboard from having performance issues. This includes being limited to a single data source from a dashboard and caution regarding Row Level Security, which can have significant impacts. I'd recommend starting with the following link.docs.microsoft.com/en-us/power-bi/desktop-use-directquery#benefits-of-using-directquery. Hopefully I'm not too far off on what you were looking for.
Regards
