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.
How would you teach X to undergrads?
Why computer scientists do X when Y happens?
Is theoretical computer science part of pure math?
How long will it take to settle P vs NP in your opinion?
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.
What is the main idea behind Razborov-Rudich natural proofs?
What are the obstacles to prove a super-polynomial lower-bound for SAT?
Where did the idea of Domain theory came from?
What are the main objects and constructions used in crypto?
Is there a program to settle Unique Games Conjecture?
Is polynomial time Turing computable the right definition for feasible computation?
What evidence do we have for Church-Turing thesis?
(sorry for the bias in my examples.)