In at least some cases, using a single consonent could indicate that the vowel had a hard sound - like if the word ended in an e - whereas the double consonant indicates that it's a soft sound. This is particularly true considering that a word that ends in e is likely to lose the e when its turned into a gerand (and ends in ing).
For instance, rake becomes raking. If it had become rakking, then the a would have had a soft sound instead of a hard one, thereby changing the pronunciation.
So, generally-speaking, the fact that it's a double consonant instead of a single consonant indicates that the vowel is soft. Now, English being English, such a rule is not applied 100% consistently, but in the three examples that you gave, you can see that the double consonant isn't needed.
Having a single l in labeling would not imply a hard e any more than it would in label. Having a double b, however, would indicate a soft a, so there's only one. The same goes for maddening. You wouldn't have a hard e would only one n, so the double n is not necessary. However, because a is soft, you have two d's rather than one. In the case of booking, there is no hard and soft oo sound, so only the one k is required.
So, the general rule has to do with making sure that the vowel preceding the double consonant is soft. So, in words where the vowel is hard or it's not the first vowel and is soft regardless, only a single consonant is required.