Documentation/config/sparse.txt

sparse.expectFilesOutsideOfPatterns::
	Typically with sparse checkouts, files not matching any
	sparsity patterns are marked with a SKIP_WORKTREE bit in the
	index and are missing from the working tree.  Accordingly, Git
	will ordinarily check whether files with the SKIP_WORKTREE bit
	are in fact present in the working tree contrary to
	expectations.  If Git finds any, it marks those paths as
	present by clearing the relevant SKIP_WORKTREE bits.  This
	option can be used to tell Git that such
	present-despite-skipped files are expected and to stop
	checking for them.
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The default is `false`, which allows Git to automatically recover
from the list of files in the index and working tree falling out of
sync.
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Set this to `true` if you are in a setup where some external factor
relieves Git of the responsibility for maintaining the consistency
between the presence of working tree files and sparsity patterns.  For
example, if you have a Git-aware virtual file system that has a robust
mechanism for keeping the working tree and the sparsity patterns up to
date based on access patterns.
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Regardless of this setting, Git does not check for
present-despite-skipped files unless sparse checkout is enabled, so
this config option has no effect unless `core.sparseCheckout` is
`true`.