It was only later that variations came into play. It allows fewer people to handle more bells, which is handy for smaller groups. It allows ringers in the 6s, for example, to pick up and play the 7s simultaneously when needed. Having additional ringers on the 7s, if they don't play throughout the entire piece, makes for bored ringers, and bored ringers cause trouble. Each has its advantages and disadvantages.
Different people choose different techniques depending on what they've learned and what they like.
Learn them all, and choose which you like best. The former, to the best of my knowledge, was invented by the ringers in Campanile . At the very least, while it may have been independently created by other ringers as well, Campanile has been the most vocal in advancing the technique, so they get the credit. To form this 4iH, hold one bell in the standard ringing grip. Open up the index and middle finger and grasp the handle of the second bell as close to the collar as possible.