For me it really depends on what the question is - if I was in the middle of coding and someone asked me a coding related question (especially about whatever we were working on) then that really wouldn't require a context switch.
However, if someone non-technical comes and asks me something (which usually requires a lot of parsing) then that will require a context switch and I will loose a chunk of productivity.
Some of it for me is pure selfishness. I just care a lot more overall about having an interesting day than being productive. An interesting day includes work and solving problems, but it also includes conversation on both technical and random human topics, connecting with people on a deeper than working level, and just plain screwing around. Luckily this all tends to balance out (at least), because maintaining high spirits and an active imagination gives a boost to productivity that's at least as strong as having a private office and slogging away in it stoically every day for 10 hours.
However, if someone non-technical comes and asks me something (which usually requires a lot of parsing) then that will require a context switch and I will loose a chunk of productivity.