Increase the fermentation? Not really. But, you should always pitch the correct amount of yeast for each batch. What I mean is this- the yeast (even one package) will ferment the sugars available. But, if it's a high OG wort, or a hot (or cold) temperature ferment, etc, the yeast can become stressed and that is a big cause of off-flavors in beer. Not only off-flavors, but stuck fermentations and a higher FG can result from underpitching the yeast. There is also a risk of overpitching, believe it or not. Most homebrewers can't really overpitch, but it is possibly especially in breweries.
By pitching the proper amount of yeast, whether it's one, two, six packages, you are ensuring good yeast health.
To find out the proper pitch rate, check out this link: Mr Malty Pitching Rate Calculator