Assume a horizontal scrollview is being populated with 2 views, leaving 80% of the scroller empty.
Should scrolling be disabled? Allowing the user to scroll makes the 2 views move without a purpose.
Not disabling the scrollbar tells the user "scroll there might be more" even if there is nothing more. I have user tested a product recently where the scrollbar appears enabled and people did click the scrollbar even when the page wasn't filled with the items completely. You could also hide the scrollbar to make it more obvious that there is nothing more.