Significados de ply a trade em inglês

I ply a trade.

It happened, on a time, there lived in that valley a lazy lad, who would neither till his fields nor ply a trade.

What are the advantage and disadvantages of plying a trade where you sleep and eat?

His recent American success has seen him plying a trade in playing dirty rotten scoundrels; stinky scruffbuckets you'd cross a county to avoid.