Samsung one huge memory maker just by itself ; but if its plans come to frutify and it manages to buy Sandisk - its going to be one hell of a behemoth in the industry. It would be by far the biggest memory maker and thus be able to dictate not just which formats are popular but also how the future memory market plays out. Flash memory has kept on becoming more and more important since it came into being and Samsung seems to have gotten a good idea with buying out Sandisk.
Sandisk might not be too averse to a buy out either considering that the company lost 50% of its market cap since June 2008. All thats needed is for Samsung to name the right price and the deal should be through.