What's the intended difference between these two tags ? My question is motivated by the comments on this question. I tried trolling MO to discern the difference, and have failed so far. And no, "you know it when you see it" is not an acceptable answer :)
How about this:
soft: "having a bland or mellow rather than a sharp or acid taste"
big-picture: "the entire perspective on a situation or issue —used with the"
A soft-question is subjective and argumentative without a precise answer and can be a question about theoretical computer science rather than being a question in it.
A big-picture question is higher-level question, and although it can be subjective and argumentative it does not need to be, and is a question in theoretical computer science.
(sorry for the bias in my examples.)