Currently working in a gas compressor module project. As always there is an anti-surge loop with an anti-surge control valve in our module.
Some collegues of mine insist that there should be straight pipe runs (e.g. 6D/4D) on either side of the control valve. It is referred to as good engineering practice. Nobody has come up with a reference to specs, standards, guidelines or the like. I have searched the literature on contol valves that I've come across. No mention of straight runs. Until the oppsite is proven I consider the requirement as a rumor.
I've never seen an actual "don't do it" recommendation, but you must take piping geometry into account in calculating valve characteristics to prevent possible cavitation. 
There's a good discussion of this in the Emerson/Fisher Control Valve Handbook.  I couldn't quickly find a copy to post for you, but I'm betting it's available online from Emerson...

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