In a situation where the screening is done by the airline (their contractor), the airport authority, or law enforcement you have basically two choices. Answer the questions completely and fully, or don't fly, enter the building, or whatever they are guarding/protecting. Actually their is a third option. They may subject you to the full monty screening. It all depends on the desired result of the screening. If it is to determine who gets a secondary or closer look their may be no "real" harm from not answering other than a secondary. However, if it is used to determine who gets to fly or not, then you have to answer if you want to fly. At least from what I remember in TLV, or any other Israeli flight. The interviews are done prior to even getting to a ticket counter to get a BP. So if you refuse to answer the questions you don't get a BP. I also remember if you had a pre-issued BP you had a special area to go to so that you could get the sticker on the BP that allowed you to go to immigration and security. My feeling is that BOS uses it to determine who gets secondary/further consideration. This is very effective if the people are well trained. If they are not well trained then it is a giant disaster ripe for abuse.