“It increases the cost, decreases the reliability.”
Turbos also usually mean that more expensive oil and/or more frequent oil changes are specified.
“Turbos add weight, add complexity, add cost and increase power. IF you keep it off the boost as much as possible, the smaller engine will give you better fuel economy but be available if you need it.”
The “IF factor” is all-important, IMHO.
For many folks, the temptation to feel the engine spool-up with that turbo boost will lead to more use of the turbo boost than is healthy for an engine.
I compare the addition of a turbocharger to the use of amphetamines.
Both have the potential to boost performance, but both also have the potential to drastically shorten the lifespan. Just because somebody can run faster or jump higher, or have slightly more endurance with the use of amphetamines, that doesn’t somehow make them healthy for a person, just as a turbocharger can make things…unhealthy…for an engine.
I know that I may not have the choice in the future, but for many years, my choice has been to pay the cost for a larger engine that has very good power when I need it, but that also tends to run at lower RPMs than a smaller turbo-boosted engine with the same power output.