QUOTE
or. Airways "ABC 123, maintain present heading"
a/c "maintain present heading thats ahh ahh radar heading 327 degrees ABC 123"
Why not "Wilco, ABC123" thus saving loads of chat?
UNQUOTE
Because it is helpful to know what the heading is so that if necessary the guy you are on a heading against can be put on a relevant one as well.
Otherwise it becomes the following:
'xxx Report your heading'
'xxx Heading 125 degrees'
'xxx Continue the heading (125 degrees)
Also if you are asked to continue a heading and report it: PLEASE do report it!