@izzythepush,
A suggestion, something implied, is not as strong as something expressed, and because the nuance, and what it suggests, is so slight it could easily be negated with further context.
I saw him climb over the wall( suggests a snapshot,)
I had been watching him for a number of days and watched his ascent from start to finish. ( This sentence changes the nuance completely, it's not at all vague, it's expressed, not implied.
I saw him climbing over the wall ( suggests some duration.)
I briefly looked up and saw him climbing over the wall, a split second later he was gone. ( Again the second, expressed non vague sentence changes the nuance.)
Hope this helps, but as Tsar said, there is no real discernable difference.