The big things are the post processing effects, render to texture, water effects, profiler, occlusion culling, HDR, and the custom splash screen. The most obvious difference for new users is the water. Pro water looks almost real, while Free water looks cartoonish. Occlusion culling can really help performance on a large scene, because it reduces the amount of stuff the GPU has to draw by not rendering anything that is hidden behind something else. Full screen post processing image effects can help add the final bit of polish needed to make something look more like a AAA game.
Without the profiler you’ll be guessing in the dark trying to tune your game’s performance. Especially on mobile. It will be near impossible to figure out sometimes. Even if the profiler was the ONLY thing that was different, I’d still buy pro as soon as I had the cash.