The Poke Assists, as they're called, are an interesting wrinkle, but in most cases faster scribbling will always win the day. Capturing Pokemon will not only place the creature by your side, but also nets you experience points that will increase the damage your Capture Styler can take and increase the length of the line you can draw. Fortunately, the developers were aware that Pokemon Ranger's fundamentals couldn't support a particularly long game, and as a result the game's pacing is snappy and it all ends before you can get bored of it.
The main story takes only about 10 hours to complete, and catching them all and completing the optional missions stacks a few more hours on top of that. For many, the game's most lasting contribution to the Pokeverse will be that it was the sole means to acquire the legendary Pokemon Manaphy, which will someday require attending a physical Nintendo event, in addition to completing the game's main story.