It has almost nothing to do with tense as we writers use the term.
The use of tense in writing exerts a force on the area encompassed by the story: it allows the author to pull and stretch and pull some more on the elements in play, on the characters, on the situations contained within – pull them to the point of breaking and see how things play out. Tenses dictate the level of connectedness between reader and story; they direct how much meaning is taken from the words, and what kind.
Past tense gives you a distance that is at once safe and encompassing; you know, when a story is in the past tense, that there is an end in sight – even if it is a bad one, there is an end, and that kind of knowledge builds that much-sought after element: anticipation.
Present tense gives you an immediacy, a sense of closeness to the action at hand, and is inherently unsafe; there is no telling if the story will end, let alone how. This kind of stress gives the reader a different kind of anticipation, one more akin to anxiety that that awaiting of predicted satisfaction. Also valuable.
This came to mind as I was reading John Green's Paper Towns last night, and I was jarred (and then pleased) when the tense being used changed mid-chapter. If I have read other books which contained multiple tenses, I can't remember them, so in this case, I felt floodgates open: there is possibility here. Obvious possibility, I guess, but possibility. The way Green uses tenses pulls the reader in different directions, keeps us on our toes – there are times when the story seems safe, when there is the comfortable past-tense distance; then there are times when the unknown is made tangible by the yanking into present-tense.
I don't think anything I am writing now has the kind of presence that Paper Towns has, the kind of stressed story that would require shifts in perspective to test the tensile strength of the characters, but I like seeing the possibility.
What about you, ether? Got any tensile strength/writing anecdotes for me?