My Foolish friend Ryan Fuhrmann smartly pointed out that once a company gets to be the size of GlaxoSmithKline (NYSE:GSK), sales growth can be hard to come by. But there are also some important benefits to being so big.

Because of its size, GSK can afford to amass the brightest scientists and the biggest drug pipeline in the business. Whereas other drugmakers may have to put a halt to large-scale testing of potential blockbusters or partner these compounds out due to development costs, GSK can afford to keep these drugs in-house and to reap the full economics of its product approvals. Investors only have to look at how long PDL BioPharma (NASDAQ:PDLI) has had to delay phase 3 studies of its very promising heart failure drug Ularitide to know what I mean.

GSK's size and the geographic distribution of its sales also ensure that investors are insulated from political health-care scares in any one country. In 2006, its U.S. sales accounted for just over half of all sales.

Even with this size, GSK's top compound, asthma treatment Advair, is growing at double-digit percentage points year over year. Not many pharmas can boast of having a $6 billion drug growing at this rate, and this just goes to show that GSK's size is no impediment to continued sales growth. Even if GSK can only grow its top line at the rate the overall health-care products market, which increased 8% last year, is growing, this is still solid growth.

One precocious Foolish analyst recently said that once a company's market capitalization is more than $100 billion, that company is effectively dead to him as a potential investment. Investors who take this sentiment with GlaxoSmithKline would be missing out on the chance to own one of the best-run companies in the most exciting industry.

Wait! You're not done with this Duel. Go back and read the other arguments, then vote for a winner.

Fool contributor Brian Lawler does not own shares of any company mentioned in this article. GlaxoSmithKline is an Income Investor recommendation. PDL Biopharma is a Rule Breakers selection. The Fool has a disclosure policy.