SQL Gotcha: convert-to-varchar defaults to only 30 characters

Converting a varchar to a varchar trims to 30-characters:-

select '0123456789112345678921234567893123456789ExtraStuff'

Returns:-

0123456789112345678921234567893123456789ExtraStuff

But:-

select convert(varchar,'0123456789112345678921234567893123456789ExtraStuff')

Returns:-

012345678911234567892123456789