Really great question, @mary25! Thanks for bringing it up 
While I’ve spent a lot of thought about how I perceive Black/Dark Magick in my own personal practice, I haven’t laid clear lines on beneficial casting for others. Like @Amethyst, most of the spellwork I do is on/for myself. The one big exception to this is for the coven’s Energy Exchange Circle (where healing/positive energies are shared at the request of a coven member).
When I think about it, I don’t think I would feel the need to ask for consent before casting helpful or protective magick on a close friend or family member. After all, I wouldn’t feel the need to ask them before helping to do the dishes/laundry/other helpful tasks. We’re close enough that I would just jump in and lend a hand where I thought it was needed- so why not with magick too? 
As for casting on strangers/people I’m not close with… like others have said, it would be a case-by-case basis depending on the situation. While it’s hard to see any downsides to casting loving and positive magick, if someone found out you casted on them without their permission I can understand how that might be seen as invasive.
I guess TLDR: listen to your heart and do what feels right to you 
This question is a great thing for every witch to consider how they would handle- thanks again for bringing it up, Mary! 
