Many businesses ask people for all sorts of personal information that is truly unnecessary for performing the function for which the person has approached the business. In some cases, the same is true for doctor's offices. Provide whatever information is needed - but, resist the temptation to provide extraneous information. In some cases, businesses may pay you for the data - usually in the form of discounts (e.g., via frequent shopper cards that track purchases to a specific person at a particular address) - in which case you need to weigh the pros and cons of supplying the information, and make an appropriate decision. Remember: Businesses do not normally give you discounts out of kindness - they want your information.
When you delete files on a computer or smartphone the contents of the files are not truly deleted - they just disappear from being seen by the operating system, but remain partially (or even fully) intact in memory or on disk. In some cases, even if they are totally overwritten, they may still be able to be restored. As such, if you are going to recycle or sell an electronic device and cannot remove the storage before doing so, make sure to wipe the device using specialized software designed for this purpose. (For information on how to do so for smartphones - please see the article How to Securely Wipe Your Smartphone's Data.) Of course, removable storage media - such as microSD cards - should ideally be removed from any device that you are going to give to others; if you must part with the media, make sure to wipe it as well.