Would help unclutter the world file. Reproducible: Always
So what you want to do is: 1. echo net-dns/bind tools >> /etc/portage/package.use/foo 2. emerge net-dns/bind instead of: 1. emerge net-dns/bind-tools
Essentially, yes. Since the two packages are part of the same software, it makes sense in my oppinion to utilize the tools USE flag.