if your going for aftermarket turbo dont over do it as most cars cant handle the excessive power and neither can the transmission. most of the time you need to upgrade the engine parts (rods, valves, etc), get a larger exhaust, stronger clutch and flywheel, sometimes larger injectors and stronger fuel pump. if you look for say like 30-100 more hp get a fairly small turbo and the engine should be ok on stock components.
most of the time turbo jobs are done cheap and wrong and cost more over time due to failing parts.
so pros:
easy power
lots of power
cool noises lol
little engines can make big power without using as much gas as larger ones
cons:
expensive
require knowledge for installation
can reduce factory engine reliability
consume a little more gas
might void factory warranty