Why should you import demo data?
Importing demo data is one of the great feature of WordPress themes. Not all themes have this feature but most of the Premium and only some few free theme has this feature.
By importing demo data you can make your site look completely like demo shown on the theme within few minutes. This will help you to understand functionality and usage of theme easily also this will decrease your development time. Once you import demo you can replace it with your real data and make stunning sites within few minutes.
Unable to import demo?
If you have theme which has functionality to import demo but even after waiting long enough you are unable to import demo, then there are few things you should do to quick fix this issue.
Disable Plugins: Most of the times error occurs due to some of bad plugins so disable all of the plugins and try importing demo.
Inspect Your Site: While importing demo inspect your site, to do this on chrome
Right Click >> Inspect
Click on Console and wait for a few minutes, if you got 500(internal server error) immediately contact your server provider to increase max_execution_time in your php.ini file
Theme Author: Even after above steps if you are unable to import demo then contact the author of the theme to fix this.