One of my main reason for using crunchy rules is consistency. While I can remember what obscure task King Palanon did in the 2nd century, implication of the Aerdy victory in 0 CY, I don't do so well with rules. In wargames I am always looking through the rulebook to make sure rules support my strategy.
I am also a realism fan. I like RPGs that are more "Realistic" than those that are not. I know a lot of people sniff at RPGs ever truly simulating reality. A lot of their points are valid. But what they miss is the idea that when designing a game it is perfectly valid to say design choice A feel more realistic than design choice B. The result still not perfect. But the end result is a game that feel more realistic.
Why is consistency so important to me? Because I run sandbox campaigns. By being consistent players can make plans for the future based on the what they know now. If they were dealing with a DM that was all over the place in his rulings then that become much more difficult. A leap from a 20 foot cliff may result in one thing this week and another the next week. Note that most DMs are far more consistent then my trivial example.
It is also partly a result of my reaction towards certain DMs in my hometown 30 years ago. During the late 70s and early 80s it was common for DMs to allow players to bring in characters from other campaigns. In many way it is like one of the RPGA's living campaigns but without any formal oversight. The result was a crazy as you think it would have been. DMs that friendship gamed were a real problem when their players tried to bring characters to other games. By the late 80's, the spirit behind sharing characters between multiple campaigns was long gone in my town.
My reaction to the whole mess was to become a by the book DM. Players coming to my table knew what to expect as I followed the AD&D rulebook as closely as I could. For the most part this worked out well despite some clunky sub-systems in AD&D. In some ways I was a contradiction, a by the book DM that allowed free reign for the players to wander my world.
In later years I found that, regardless of rule systems, that going by the book seems to liberate my players in some ways. By having a firm set of rules from the beginning they feel more comfortable in coming up with interesting plans (combat or non-combat) as they can assess the odds. It was never a sure thing as they still had to succeed on the various dice rules. Taking a calculated risk is a lot more fun than a blind stab in the dark.
And there are negatives to this approach. The first is excessive rules look up, I have been chided numerous times by my players "To just make it up". I have overcome this somewhat both by making up good reference sheets and by loosing up. The second is the learning curve associated with learning a crunchy set of rules. To a new player a crunchy rules set is just as much of a stab in the dark as a rules lite system that relies on GM fiat.
Even after three decades I am still evolving my approach to deal with this issue. For the most part I can make it work but I still miss the boat at times and totally turn off a player to a new game. What I do is run a example combat with the character they made up. I also allow them to freely change their character with no questions asked for the first few sessions. The implications of a crunchy rule system take a while to sink in. Finally I have a golden rule "Don't be a jerk about the rules."