The copyright law defaults to author control of copying, modification, and distribution, so others need the author's permission to copy, modify, or distribute. If you would like others to be free to copy your software and possibly build on it, then you should choose a license. Open source licenses give the permissions needed to get that default copyright impediment out of the way.
Some of the products that appear on this site are from companies from which QuinStreet receives compensation. This compensation may impact how and where products appear on this site including, for example, the order in which they appear. QuinStreet does not include all companies or all types of products available in the marketplace.