In QTP, very often we call use Reusable Actions. While calling them from main script we always use absolute path to locate it (shown in the pic like D:\QTP\ReusableActions)
But when you use absolute path we might have some problems when you move your scripts to different location(may be different drives/machine).
However such problems would be avoided if you use Relative path.(shown in the pics like ..\QTP\ReusableActions)
Hope this would be useful to you.
