It won't affect low level characters or shouldn't.  But Rule 3: The Laws of Realism.  This also means, unless you obtain or your character later in his/her adventuring career creates an enchanted spellbook, wizards won't be carrying their entire spell library in a single book.  So for higher level wizards, as they collect spells and expand their repertoire they'll need to possess multiple spellbooks.<br/><br/>Now of course most adventuring wizards usually end up, spending  the time to write a separate book for taking on their travels.  While this may at times limit them in certain situations, and find them cursing because they could have had a spell for something with them, most wizards would also rather not carry entire libraries (nor do they have the means to do so).<br/><br/>Other more specific examples of Rule 3.  Keeping closer watch on how much people are carrying, including coins and other treasures.  And while I won't implement a crazy and tedious, fatigue system like was introduced with the Player's Option system in 2nd edition.  Let's be a little more reasonable, people aren't going to fight all day and all night and still be jumping and down.  Or even just traveling all day, one can't be expected to be ready to run a marathon.<br/><br/>Again as mentioned before, Rule 3 exists to bring that slight semblance of realism to a realm where magic and heroic deeds reign.  You're still the hero that can try to jump over the gap or pull yourself up on a ledge with one hand, because you're fighting off a demon with the other.