The opposite effect applies to imports; they become more expensive when your currency is strong. The net welfare gain is thus small if there's any.

Artificially boosted competitiveness tends to lead to trade surpluses. Trade surplus = net capital export = not available as capital investment or consumption at home = you basically work for the quality of life of others, in exchange for a mere promise to be paid back sometime in the future.

Promises are being broken at times (just look at a certain country that's known for its series of very much lying governments), and even if there's no promise; a capital investment in a foreign country can go wrong and yield no capital income, thus be wasted.