I am using hotmail
1. Personally I think it a mistake to disable/uninstall the Mail Shield even if don't use an email program, but use web mail viewed through your browser. In fact I would suggest you leave it installed as it isn't using resources unless it is actually running and I would go further to suggest that you set the sensitivity to High.
The reasoning for this is, if you have a trojan spambot (they have their own SMTP program), which has got past your defences, either undetected or hidden; then your first indication could be the alerts from the Mail Shield of this activity.
2. As for P2P if you have no P2P applications and have no intention of using P2P, you can remove it (not just stop it). Control Panel > Add Remove Programs or Programs and Features, Select avast > Change/Remove or Uninstall Change. You now get an avast windows, selecting Change and click the Next button, there you can uncheck the P2P shield.
Should you decide to use P2P at some point in the future you can reverse the process.
I have removed P2P and IM shields as I don't have any of those applications and have no intention of doing so. As has been said you will save very little in hard disk space or resources used (as the shield wouldn't be active), but I do it as it removes them from the avastUI listings in the Real-Time Shields, etc. I'd rather have the screen space.