I'll warn you right off, I have a very bad attitude about perineal massage.
It's my opinion that with warmth, privacy, patience, and giving oneself over totally to the process, the perineum will stretch as much as it needs to, and that it is exposure to the (relatively) cool drying air, and inhibition and discomfort, and being coached (which keeps one from going within), that makes tears more likely.
All of these things go along with perineal massage.
In my case, I had it done with my first. It was terribly painful, first of all, to have to be on my back, and pushing was difficult that way. Second, it was disconcerting to have someone down there working away on me. I could not seem to focus on anything but the pain and the fact that my perineum was the focus for everyone else in the room. I believe that my inhibition and being constantly pulled back into the reality of my attendants by their actions both hindered the baby's progress and the ability of my body to respond appropriately to the baby's movement through me. I don't think my body was ready to give birth, yet the forced pushing and stretching of my perineum hastened the birth unnaturally, so my perineum wasn't naturally and fully ready by the time the baby came out. I did not tear, but I did have a "skid mark" that burned every time I urinated for several days, and my perineum felt bruised and swollen for days as well.
For my second and third births, no one was allowed to touch my perineum. Because I was laboring either in water or in an upright position either with my legs together or sitting on something, my perineum stayed warm and moist, and probably most important, much more relaxed than if someone I was not normally intimate with was touching it. (Not only touching, but stretching and manipulating. Not pleasant.) Without the observation and physical intrusiveness I was able to go "within" and listen to what my body needed me to do. The babies slid out quickly and easily (one even had a nuchal hand), and I had no trauma to my perineum.
I know others have had a different experience with perineal massage, even enjoying it. But I consider it an intervention, one that carries risks. I can't say that it is a bad thing for all people, but I do believe it is at best physiologically unnecessary (mentally, of course, *believing* that something will help may in itself have a positive effect,) and at worst can actually hinder and hurt.