If you are purchasing a brand new frame which hasn't had any components installed then yes, you will need the bottom bracket faced and chased. If you are just replacing a bottom bracket on a bike which already had the bottom bracket installed then you don't need to face or chase the bottom bracket shell unless it's damaged and isn't flat or the threads are damaged. It's very important that the bottom bracket shell is prepared correctly, you can't just install a bottom bracket on a shell that's not flat or has threads messed up.