Statement of Criterion
Adding a preference to a ballot must not increase the probability of election of any candidate ranked above the new preference.
Later-no-help is satisfied by Instant Runoff Voting and Douglas Woodall's Descending Acquiescing Coalitions method. Some forms of Majority Choice Approval satisfy this criterion. It is trivially satisfied by First-Preference Plurality and Random Ballot, since those methods do not usually regard lower preferences. Virtually every other method fails this criterion.
Later-no-help guarantees that the method will not use a voter's indicated lower preferences to elect a higher-ranked candidate who would not have been elected if this voter had not expressed any lower preferences.
As a result, voters may feel free to rank candidates between whom they have no clear preference equally, rather than expressing insincere preferences between those candidates which could effect the outcome of the election.
Later-no-help is incompatible with the Condorcet criterion.