Committing without locking yourself out
Commit when an upgrade, your items and the lobby point the same way. Until then, every item you finish should leave a way out.
Checked for patch 18.4. The numbers come from the live Set 18 data and follow every patch.
The idea
Committing is the moment you stop keeping options and start spending on one comp. The damage items go on its carry, the pairs that only fit something else get sold, and the next roll is for its units. The game review calls a unit your carry once it holds 2 damage items, and from that point every damage item you finish should fit it.
Commit when three things point the same way: an upgrade that defines your board, like a 2-star of a carry or of a unit the comp is built around; items that fit that carry; and a lobby where you are not behind on it, which you only know by scouting. One of the three on its own is a lean, not a commitment.
Commit too early and you can lock yourself out. Every finished item fits fewer comps than its components do. Among the 71 current comps, Recurve Bow fits 66. Finish it into Guinsoo's Rageblade and 37 still use it, only 24 on their carry. Commit too late and you pay the other way: health lost to a board that is half of two comps, gold tied up in units that never fight.
Until you commit, finish the items that win fights now and fit many comps, and keep the components that would only fit one carry. Defensive items are the safest to finish early, because every comp needs a frontline.
Once you commit, keep one way out: a second carry that uses the same kind of items, or the comp's flex slots, which take whatever upgrade the lobby leaves you. The game review marks the two ways committing goes wrong: a board built for a comp whose carry never showed up, and damage items that do not fit the carry holding them.
See it live
Pick a component and read what finishing it gives up: how many current comps use the component, and how many still use each item it builds.
The component you hold
Recurve Bow66of 71 current comps use it, held as a componentFinish it, and the comps that still use it
Guinsoo's RagebladeWith Needlessly Large Rod37comps, 24 on the carry
Last WhisperWith Sparring Gloves31comps, 8 on the carry
Red BuffWith Recurve Bow25comps, 7 on the carry
Void StaffWith Tear of the Goddess22comps, 3 on the carry
Kraken's FuryWith Negatron Cloak16comps, 9 on the carry
Titan's ResolveWith Chain Vest13comps, 7 on the carry
Counted the way the comp finder on the comps page matches your spot: a comp uses an item when it builds it on any unit, early or late, and a component when one of those items needs it or the comp takes it first from the carousel.
The rule of thumb
Commit when an upgrade, your items and the lobby agree; until then, finish only the items that keep several comps open.
Check yourself
When is the right moment to commit to a comp?
Pick an answer.