If the company is shitty like Ubisoft or Nintendo
If a game looks good but has no demo and you do intend to buy it if you enjoy it.
I pirated Tormented Souls for that reason and bought it as soon as I completed it, then replayed it a whole bunch. Its made by a small Chilean team too so I wanted to support them and it worked since Tormented Souls 2 is coming out soon and they released a demo with an hour of content.