In my opinion fit up inspection, for most environments, of each and every joint is overkill, and most likely unproductive. Verification of WPS requirements as jon mentioned is certainly required by code, as with volts, amps, travels speeds, etc., but I believe that most of them assume a random inspection.
It should be up to your Manual and Inspection Procedures to determine the extent necessary, because, in the end, no matter what inspection you require, if production personnel wish to circumvent the procedure they can. At some point you always have to trust that your personnel are doing it right, unless you have an inspector for every production hand.
If you find your level of inspection is inadequate you can always increase surveillance, or concentrate on those individuals of special concern.
I think it is important that you write into your Manual that welders, fitters, etc. be responsible for their own work, as jon mentioned, and indoctrinate them as such. And then verify with independent QC inspection over the top of that.