What is the effect of not sub-vocalizing on reading comprehension? Sometimes when reading, text segments are not so important or relevant, when that happens I tend to read between lines in a visual manner, without sub-vocalizing or pronouncing the words in my mind.

Could that way of reading affect text comprehension?
Yes, inhibiting sub-vocalization is likely to impair comprehension.

Here is the abstract from Slowiaczek &amp; Clifton (1980):


  Two experiments demonstrated that subvocalization is of value in reading for certain types of meaning. Blocking subvocalization by requiring subjects to count or say “cola-colacola …” aloud impaired their reading comprehension but generally not their listening comprehension. The effect of blocking subvocalization was found to be specific to tests that required integration of concepts within or across sentences, as contrasted with tests that required only memory of individual word concepts. Two hypotheses were offered: first, that subvocalization results in a more durable memory representation needed for integration of concepts; and second, that subvocalization enables a prosodic restructuring that makes information needed for sentence comprehension accessible.


Reference


  Slowiaczek, M. L., &amp; Clifton Jr, C. (1980). Subvocalization and reading for meaning. Journal of Verbal Learning and Verbal Behavior, 19(5), 573-582.