I personally use "that" in written communication and omit it in spoken communication.

The reason is that if I had left out "that" in the beginning of this sentence, it is less fluent. Rewritten, I could say, "Leaving out the word 'that' at the beginning of this sentence is a good illustration of my point: it's less fluent," but since I so often structure my sentences with "he said," "the reason is," "I thought," and whatever other "that"-needing subject first instead of the opposite way, I use the word "that" to make it sound more fluid.

I omit it in spoke communication, because the inflection of my voice and rhythm of the sentence leaves a lot more room for implied words.