Certain characteristics depend on the "breaking" concentration rather than simply ending. To show the difference, first there is the "Concentration" section of the rules that set:
(…) If you lose concentration, such a spell ends (…)
Keep in mind that this applies to any method to lose concentration. Then there is the conjure elemental spell, which includes the following:
(…) If your concentration is broken, the elementary does not disappear. Instead, he loses control of the elemental, becomes hostile towards you and your peers, and can attack (…)
Keep in mind that Jeremy Crawford has ruled unofficially (tweeted) about this, stating:
Deliberately ending your concentration in a D&D spell is not the same as breaking your concentration. In the concentration rules (PH, 203), voluntarily ending your concentration is not intentionally on the list of things that can break your concentration.
He has also tweeted monitoring:
The distinction between voluntarily ending your concentration and breaking your concentration is only relevant when a rule tells you that it is relevant. The elementary spell spell is a rare case of the distinction that has meaning, which is detailed in the spell.
The list to which it refers is that of the "Concentration" section, which states:
(…) The following factors can break the concentration:
- Cast another spell that requires concentration. (…)
- Taking damage. (…)
- Be incapacitated or killed (…)
Therefore, it seems fair to say that the concentration can end but not break, for example, if a caster decides to stop concentrating on a spell.
The section on "Longer Release Times" only tells us what happens when the concentration is broken:
When you cast a spell with a longer casting time than a single action or reaction, you must pass your action each turn to cast the spell, and you must stay focused while doing so. If your concentration is broken, the spell fails, but you don't spend a spell space.
It doesn't explain what happens when your concentration it ends but it hasn't broken.
So what happens if you are casting a spell with a longer casting time and choose to stop concentrating? Or maybe the premise is flawed, and stop concentration on a spell like this make tell how to break your concentration; If that's the case, I'd like to know too.