Empty Solder Points On PCB?
There could be several reasons for having solder pads that aren't used:


Test points - these are pads that are used to connect test equipment to the board to test it in the factory.
Unneeded parts - the board was designed, then it was discovered that you could leave out some of the passive parts (resistors, capacitors, inductors) with out causing problems.  Most often these are parts that were intended to reduce emmissions (radio frequency "noise" that can interfere with other devices.) Testing showed the whole board to be "clean" enough that they could be "dirtier" and still meet all requirements.  Leaving out specific parts can reduce the price of building the board.  They don't bother to change the board in such cases.  Alternatively, the plans include extra parts to remove emmissions, and these are only used if the board isn't clean enough.
The board can be used for multiple models.  It has sub-sections that can be left off to produce a cheaper board with less functionality.  You design one board that can be populated in different ways to produce different models.  In these cases, there may also be parts whose only job is help the electronics detect which sections can be used.  These may be as simple as a jumper or as complex as a read only memory device containing a list of usable sections.


There are probably other reasons as well.  These are the ones that pop into mind.