As a teenager, sex involves a lot of rubbing. Due partly to the sheer joy that someone was actually allowing you to kiss and fondle them, and partly to the fact that you were a bit unsure about what to do next, much teenage rubbing is done through clothes. As we get older, we forget the joys of frottage. The thrill of feeling someone who turns you on rubbing themselves against you in a sexual way whilst you are both still fully clothed. The anticipation of what is to come, combined with the uncertainty of exactly when that next step is going to take place. All that time spent rubbing and stroking is damn fine foreplay which can often be neglected once you are old enough and brave enough to just go for it.
Whether you are clothed or naked, alone or together, non-penetrative sex definitely has its own special brand of excitement. Unless you are completely averse to anticipation, there must be some excitement in knowing that orgasm is… pending.