Are shims any good for a guitar?.

Updated
mushman
I removed the neck on one of my guitars to find 2 peices of a buisness card stuck in the pocket as a shim. The tech who set it up before I got it felt that a straight neck with a shim was better than a neck with some bow in it. The truss rod adjustments need to be done with the neck off so granted it is a pain in the ass. Since a tight neck pocket and neck to body contact are critical,wouldn't a shim kill some sustain?,or is it common practice to do this?. Any way I took them out and will loosen up the truss rod a little and lower the action and see what happens.
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