Tableau, data visualisation and story telling live vs extract

what is the difference between live connection and extract?

extract is a snapshot of the data, the extract will need to be refreshed to receive updates from the original data source, whether it is a local file or an on-premise database.

Live connections offer the convenience of real-time updates, with any changes in the data source reflected in Tableau.

thanks for your reply.but can you please tell me that if i have to collect the data source from the server then which connection i should prefer?
why Extracts tend to be much faster than live connections, especially in more complex visualizations with large data sets, filters, calculations, etc.?