Could be a address collector (not sure what they get out of that) or a client that is taking transit and needs to "plot his travel" you just never know. I have hit many that an intersection is not enough for them to to work out buses so an alternative I have is giving postal code. You can map it on iphone and google maps which gives a close enough location without giving your house/condo number.
If in doubt, block. If maybe ok, intersection. Alternatively postal code. Always err on the side of caution. Trust your spidey senses, if its to good to be true.....