This question is loosely related to Why some plugins are including wp-includes/plugin.php file?

What I’m trying to figure out is, when is it smart to include this file, and when isn’t it?

I’m building a plugin that’d need the is_plugin_active() function in the frontend (where it doesn’t exist, because it’s only loaded in wp-admin.

My gut says it’s a waste (of memory or performance, maybe?) to include the entire wp-admin/includes/plugin.php just for the purpose of loading one function. So, IMO, a better idea would be to copy the is_plugin_active() function to my own plugin and run it from there.

Am I right about this? Or would you say: No, just require_once() the plugin.php file — even if you only need one function from there? And if so, why?