Before modifying an existing line of code, understand what it's purpose is/was. Even if it doesn't appear to have one, or make any sense, someone created it for

Before modifying an existing line of code, understand what it's purpose is/was. Even if it doesn't appear to have one, or make any sense, someone created it for a reason. Also IDE/search tools for determining where a function is used are great for removing stale, unused cruft.