pros: they benefit domestic producers of that good. b/c there are less imports competing with them.
cons: they hurt consumers of that good through higher prices of imports or lower quality of domestic goods.
Another con is that domestic producers have no incentive to improve quality or reduce costs, so in the long term they will still lose out to foreign good either b/c importers will establish assembly plants inside the country (this is what happened to Big 3 Automakers), or price/quality gap between domestic and imported goods will become so large that even quotas would not help (as it happened with clothes manufacturing in US)