This is a late response but I think it can help to understand.
jimport is the first loader (if we can tell) of Joomla 1.7 to 3.0.
Here is the definition of the function taken in Joomla 4:
* Intelligent file importer.
* @param string $path A dot syntax path.
* @param string $base Search this directory for the class.
* @return boolean True on success.
* @since 1.7.0
* @deprecated 5.0 Classes should be autoloaded.
or JLoader::registerNamespace() to register an autoloader for
* your files.
function jimport($path, $base = null)
return JLoader::import($path, $base);
So you can use
jimport until Joomla 5 without problem.
To respond to the question, it's required. If in the version you develop something doesn't work, it's because some classes like
JFolder are not loaded (include() or require(), the classic/old way to load a class on older versions) because there is no need in memory if it is not used.
So first use
JLoader on 3.0+ for future compatibility and use old
jimport only on older versions 1.7-3.0 if you can't update to the latest for some reason.
As say in the documentation for Joomla 3+ :
JLoader::registerNamespace() to register an autoloader for your files.
JLoader::register() works but it is also deprecated.
It is useful also to register your own libraries.