Absolute paths are not portable between applications. If you
move the application that the absolute path points to, the
links will break.
Relative paths in the style of client elements can be
difficult to maintain if you move resources or pages to
different folders.
To overcome these disadvantages, ASP.NET makes available the
Web application root operator (~), which you can use when
specifying a path in server controls. ASP.NET resolves the ~
operator to the root of the current application. You can use
the ~ operator in conjunction with folders to specify a path
that is based on the current root.

~ is used to call destructor also

"~" is used to represent the current application folder in asp.net