You can build an Urtet deck in a myriad of ways, including artifacts (affinity, metalcraft), tokens, proliferate, or ramp
Greens Exploration adds both playability and aesthetic appeal
In fact, the Blogatog post we referenced above was in response to a question on that very subject
The main one being that if you have enough dark types for it (which you will if you're playing a dark type deck), you can use his ability to put 8 dark type Pokemon onto your bench, making for a whopping 9 Pokemon in play
I can see the card advantage aspect of this, as youre essentially drawing up to four extra cards every time you attack with Pako, but Ive played the decks that draw excessively and they are just not for me