Playing this type of opening allows me a chance to get a feel for the player's strengths and weaknesses, does the player like tactics and does he or she know how to play a positional game (i.e. pawns). The London System is not suited to someone who wants to obtain and keep the opening advantage; it is more of a 'wait and see' opening; however, if you give me the advantage in the opening I will gratefully accept it. The opening allows you to get to a middle game without too much thought, where you can start your heavy thinking. Think of this opening as a tool to use when you are playing someone you do not know, and you want to gather information about his or her playing abilities.
To be fair, Capablanca, Reti, Alekhine, Kamsky, Tony Miles and Kasparov played this opening in their careers, so it can not be all bad!