Umm Naruto is actually doing that not Sakura ijs
Naruto only did that for shikamaru when the slugs sakura summoned died
But he did not heal ALL the AS
See here before the god tree attack sakura heal everbody on the shiniobi alliance
She tells katsuyu to attach to everybody
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After the god tree attack
Sakura slugs pieces died so she wasn't able to use remote healing
Than naruto save shikamaru
But after that
Tsunade and sakura summon another slug
And start doing regeneration (not simply healing)
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And
Few chapters later
Constantly healing because the alliance were still fighting and hurt themselves again .
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You can clearly see her healing .