This is one of the best descriptions of what happens during the Rosary, and praying for someone, I have read (not the full picture, but just a wonderful aspect of the whole):

"When you pray the Rosary for someone,
Mary places that person between you
and her.

As soon as you start, you radiate currents
of love to Mary. She instantaneously re-
sponds, by sending currents of her love
to you.

Currents of love simultaneously radiate
from the both of you, and the person for
whom you are praying gets caught in the
crossfire of your love. If that person is
like a wilted plant, the currents will prop
that person upward..."

"The Crossfire of Love" by Patrick Pontillo