Widening the ports adds volume to the cylinder. For a given piston velocity, there is a given amount of mixture of fuel and air that will flow. With a wider port, comes a decrease in pressure. At lower piston speeds, this decrease in pressure can decrease the amount of fuel and air that will enter , assuming the width is consistantly enlarged from intake to the cylinder. At higher piston speeds, the volume lends itself to more easily allowing more mixture to flow.
When you add intake timing, you allow more mixture to enter the cylinder earlier in the cycle. This can facilitate more mixture into the cylinder for a given piston speed.
However, there are a LOT of variables. For instance, if you only add intake timing and do not increase the size of the intake port at the carburetor, you will generally increase torque to a point, as you have now increased the rate of flow over time so that the cylinder fills up better(it's also likely add torque at all rpms on most modern saws, actually). If you increase the timing AND increase the size of the intake of the cylinder port at the carb consistently towards the port, you will decrease velocity at lower RPMS and facilitate more flow at higher rpms. Etc.
Unlike automobiles, saws have a very limited means to change their 'gearing' - sprockets, to a small extent - chains, and bars. So how one times and modifies the ports is very important.