Well, when doing spell work or ritual I would always ask permission first even if I am asked to help. Asking and giving permission is two different things, even though so slight.
I give positive energy to whoever wants it. My friends joke calling me the "Smiling Pagan" sometimes. Being a fire element with a fire sign it makes it hard for me to keep my cool at certain times, especially if a friend or relative is being hurt or feel like they are being unjustly attacked or yelled at. I send protective energy or "incase them" in my own to help and I usually do not ask permission (when I know I should in some cases) but I am also tender hearted and can feel emotions of others and the momma in me wants to help. If someone tells me they have a bad day or are going through something like a surgery or severe depression I let them know that I am putting out positive energy for them and when they need it they can just tap into it if they need it. But I believe that the gifts the gods gave me were for that purpose and many of us, like myself, were given these for that purpose.
Also, you can sit or stand in an area, away from people like at a party or even a store, and call up positive energy around you. Without saying anything to show that you have and people will automatically gravitate to your area. Why? Because, it is a positive in an area of negative influences natural and synthetic. So, personally, I do not believe you need to ask permission to send positive energy, if they want it or when they need it they will take it, even subcontiously.