You gave 2 examples where vpn make sense - circumvention is the key... If what you are looking to protect yourself is your isp saying hey you can not do that p2p because you shared xyz whatever. Ok then sure vpn works..
If you want to circumvent some geographic restriction, again sure vpn can make it look like your coming from region A while your really in B..
But lets be clear here - your not protecting yourself ;) Your hiding shit you could get in trouble for or trying to break someones policy on where you can come from.
So you policy route your this traffic, and this traffic only. If your son wants to p2p.. then policy route his p2p traffic out the vpn. If you want your media player to stream something from region B, then policy route that connection out vpn in region B..
Lets be honest here, your not "protecting" yourself from big bad isp here ;) To be honest if you want to download p2p stuff you be much better off getting a seedbox somewhere in a country that has lacker laws and doing it all there, and then just use secure channels to that box to move what you want to and from it, https, sftp, etc.
Routing all your traffic through a vpn is just nuts.. Paying some company X$ to protect you is nuts - better off just getting a box somewhere else and routing/doing what you want to do that is ?able there..