We like to support appropriate causes where possible, but there are limits and sometimes the cold calls get on my nerves a little when they have no connection to our business in any way and just see us as a possible soft touch.
Call it self interest, but we start with looking at how it can benefit the business to be involved - if the person requesting the donation or sponsorship is a client or represents a target market etc, then we will look at it. Otherwise we are not doing the right thing by the business, and drawing the line in any other way would be arbitrary.
If it's just an unassociated person with no connection to our business, and no foreseeable benefit, then it would normally be no - I sponsor my kids in their various school coordinated charity efforts instead.