This helps when you cut thin strips of wood, because it will keep the side of the blade protected. Instead of the entire blade guard being pushed up as a workpiece passed under it, only the part that comes in contact with the wood gets pushed up. This means the blade guard consist of two pieces (called leaves) instead of one.
The only difference that is actually good and useful is the two-leaf blade guard. The difference between the feet of the DWE7491 and DWE7492 Improved Blade Guard The original DWE7491 feet design was maybe slightly more sturdy and resistant against bumps. This makes the saw slightly more stable and less likely to tip over. The DWE7492 also has different feet (see image below), which stretch out to the side. This helps support workpieces slightly better as they move past the riving knife, but it’s unlikely to make a big difference. A 20mm wide part is bolted on at the back of the machine. The old DW7491 does have a slightly deeper table, which you can see from the images below. The new DWE7492 is 100 grams lighter and about 1 dB quieter, both of which are completely unnoticeable to any normal user. The DWE7491 and DWE7492 are almost identical. The Difference between the DWE7491 and DWE7492