I think it's one of the worst things a copywriter can do. And if your copywriter ever does this, you should Run (yes, Run with a capital "R") in the opposite direction. Copywriters, who are presumably skilled at marketing, should know much, much better anyway.
"I write about all different things. I write novels, short stories, poems. I also do copywriting."
OK, there it is: If your copywriter ever indicates that he/she is a master of all things involving the written word from screenplay writing to advertising copy, lace up those running shoes.
It's an absolutely ridiculous claim, because no one, no matter how good he/she is, can be all things to all people. If you don't believe me, go visit my LinkedIn profile and see what people have to say about my copywriting and marketing expertise (I'm pretty proud of those reviews). Then ask me to write you a poem. You'll see right away that my expertise as a copywriter does not translate into this genre.
That's because I spend the bullk of my time learning as much as I can about social media, writing sales copy and interacting with professionals in the Web development, search engine marketing and education fields. So, what I specialize in--copywriting for business clients--I do very well. But in the writing areas I don't consistently work to perfect (ficitional writing), I'm so-so at best.
So, what happens when someone asks me, "Can you ghostwrite short fiction?" Or, "Do you ever do short stories or poems for blogs?"
I tell them, "No."
I can't in good conscious sell myself as a first-class fiction writer and charge folks the industry standard rate for work I know I can't perform at industry standard. I would be doing half-assed work and secretly loathing it.
I'd much rather refer those clients to someone who does specialize in fictional writing than risk earning a reputation as an incompetent writer at best and a fraud at worst.
Many writers, I'm sure, would disagree. "The economy is tough; you can't be turning away work," or "I know it's not my first choice of writing work, but it is writing work," are definite arguments in those writers' favor.
Nonetheless, I stick to my guns; I say copywriters come out ahead by contininuing to master their chosen area of expertise (copywriting for a particular industry, learning to use social media for more effective marketing, etc.) instead of attempting to be all things to all people--even in down times. A dedicated copywriter should be focused on writing copy. Period.