Love these girls. Love the whole idea of the Wicca Group as being a great big bust. As being just, you know, "We are earthy and crunchy and useless." This scene is also, of course, close to my heart in a big way for the other obvious reason. Seth Green, who played Oz and was Willow's love interest and is a great actor, left rather abruptly. And we weren't sure where to go.
[Tara's first appearance on the show]
And then she - Amber Benson - appeared, and made up our minds for us. We had the idea of introducing the character of Tara, the very shy girl who falls for Willow. Fairly early on we had the idea that college is the sort of place where people expand or explore their sexuality, and the idea of somebody who thought Willow was great was interesting to us.
And the idea that basically, we had a new Willow. Because Willow had become so self-confident and at ease with herself, she wasn't as helpless as she used to be. And so we wanted somebody, particularly for this episode, who could act as a kind of Willow character. Somebody we would be invested in, who could be put into danger, who would not necessarily know how to take care of herself off the bat. Because you need somebody like that, and Willow - and Alyson herself - had both matured to the point where it took a lot to get them into that kind of peril.
Amber Benson obviously a mainstay of the show now, and their relationship, extraordinary. Didn't know for sure; I was thinking of somebody more physically like Alyson: smaller and... and less womanly than Amber. It was Marti Noxon, when Amber auditioned, who said - you know, she knew the physical type I was thinking of because I really wanted that vulnerability. And she said, "I think Amber's got it in spades." And so we brought her back and she knocked us out. So Marti gets the kudos for that one, although I like to take the credit whenever Amber's around: so make sure Amber doesn't hear this!
(source)