it needs to be fed with oils, old single stage paint can get very dry, imagine dropping a drop of water on chalk. your compound might dry up on the paint making it look hazy, in addition the oils revive some of the paint so you might just save some paint from getting cut.
going straight to compound with single stage is called caveman compounding.
google "restoring single stage paint, autotrader," an article by mike phillips will show up. that will tell you the deal with single stage
i gave his system a shot and it worked very well, the paint looks very wet on my test spot, i plan on doing the entire car after my exams