Consider this. Naturally aspirated engines run at 14~psi of "boost" naturally. The air that fills the cylinder on those engines is pushed in by atmospheric pressure, the same way our lungs are able to fill with air.
If you add a blower/turbocharger, and add "boost pressure", you are supplementing the atmosphere. So 1psi of boost is actually 15~psi total (at sea level). Imagine the seas drained, and we could drive below sea level, where pressure increases, you would be adding "boost", exactly the same as when we drive into the mountains, we lose "boost". You wouldn't hear anybody say "dont drive below sea level with a restrictive exhaust" if you catch my meaning.
The only thing that would concern me is if you had a built engine with a big overlap, where the increase in exhaust gas volume caused an issue where "back pressure" was impeding the flow of the intake charge and contaminating it. The exhaust should be sized to fit the application, if your application is strictly 5000+rpm drag racing and you have a large overlap and 30psi of boost on leaded race fuel, running a restrictive exhaust is probably not a good idea. But if your application is street car, daily driver, and the engine is mostly OEM, having an exhaust system that does not meet perfectly the demands at WOT (there is some back pressure) will be a good thing at lower RPM (where you actually drive your car, 2000-5000rpm) because the "restrictive size at peak power" becomes a benefit during those middle rpms, increasing the velocity of the exhaust gas, and actually exerting a pull on the cylinder helping the exhaust gas exit. You may have noticed that if you install a large exhaust system on a tiny 4-cylinder engine with no performance modifications it will lose torque through the rpm range with no other changes. This is because the exhaust system was helping to scavenge the cylinder thanks to the aforementioned velocity increase. A good read on this subject is "David Vizard" books, mostly directly at small block chevy, he found that exhaust systems sized properly can exert as much as 16 TIMES the cylinder filling pull that the descending piston is capable of.
a "PERFECT" exhaust system would start out small, and gradually increase in diameter as the engine RPM developed, maintaining exhaust gas velocity and keeping pressure down through the rpm range.
