How much enamel must be removed for bonding?

10 yrs ago, I chipped my front tooth (small sliver, along the edge, going about halfway up) and my dentist repaired it with bonding. All good until last week. My prior Dr retired and while tooth wasn't that cosmetically bad, I asked the new Dr to repair it. He did, but drilled out a SIGNIFICANT piece (about 1/6th of visible tooth!) to do so. I know some roughing up is needed, but this was a big surprise and if/when it falls out again, doing nothing will no longer be an option. Was this right?