Tooth Structure is Weak
Ask any dentist and many will tell you that when part of a wall is missing, that the remaining tooth structure is weak even when there is a significant amount of supported (underlying) dentin.
A long time patient fractured the small remaining disto palatal cusp. That cusp, whether present or absent had no measurable effect on the remaining tooth strength and yet a large number of dentists would immediately remove ALL of the remaining enamel for a crown under the guise of strengthening the tooth.
I placed an MODL composite in the maxillary right first molar 20 years ago (prior to the time that I beveled all cavosurface margins.) Upon removal of the existing restoration, I learned that there had been no leakage down the walls or on the floor. The bond remained perfectly intact for 20 years.
I removed no additional tooth structure except to place a bevel and restored the tooth with another MODL bonded composite. Someone might place a crown on this tooth but it won't be me. I would expect this restoration to last 25 years.
(Aside: I recently saw 9 of my long term patients on the same day who have been my patient for 30-38 years. Every patient has every tooth that they had when they became my patient. As a group, they had very few crowns in their mouths which is WHY they still had all of their own natural tooth. To paraphrase my friend Maurice...One tooth for one lifetime.)
Natural tooth structure is much stronger than they taught us in dental school or that most practicing dentists believe.