It distinguishes meaning in all contexts as far as I can tell.
In some words, either the voiced or unvoiced variant do not have an assigned meaning, but you must use the correct one.
In some cases, there is a near clash. For example, "thin" and "then" have a different vowel, which is clear when they are enunciated clearly. However, when it's an unstressed vowel in surrounding speech, particularly fast speech, the difference relies much more on the leading consonant, because unstressed vowels in English gravitate toward the central [Ə] sound.
There are also situations like "this'll" (contraction of this will) versus "thistle".
In some words, either the voiced or unvoiced variant do not have an assigned meaning, but you must use the correct one.
In some cases, there is a near clash. For example, "thin" and "then" have a different vowel, which is clear when they are enunciated clearly. However, when it's an unstressed vowel in surrounding speech, particularly fast speech, the difference relies much more on the leading consonant, because unstressed vowels in English gravitate toward the central [Ə] sound.
There are also situations like "this'll" (contraction of this will) versus "thistle".