They use this phrase because they do not want to say, "I Love you" but they do not want to look too uninterested by just saying , "Thank you" or "Sincerely"
So they go with something just in between that'll still give them power over the guy without losing the chase.
A sly verbal tactic for females to essentially whip the males with hope and a false sense of security and attention.
As other definitions have pointed out: women may also employ this phrase, however this is not something to scorn them for; many of us suffer from ignorance of alien-cultures.
British: Toodle-pip old chum; it's been marvelous, much love to you.
Woman: Ha, ha, that is so funny, much love Jimmy; must dash.
Italian: Il nostro amore è la cosa più importantissima nella mia vita. Io brucio per amore di voi. Tu sei con me ovunque io vada. Ora e per sempre, il mio sexy maschile, molto amore.
Joe: Shut the fuck up bitch. You were probably born missing a few chromosomes.