My friend used to do this all the time and I thought it was the cowards way out.
However, I am starting to believe its not a bad idea to do it if you are not sure of the woman's IL.
If you are unsure of her IL, she might not feel comfortable giving you her phone number. Leaving yours, it takes the pressure off and gives her the initiative. If her IL is above 50%, she will contact you. If it is 50% or below, you probably won't hear from her.
However, I am starting to believe its not a bad idea to do it if you are not sure of the woman's IL.
If you are unsure of her IL, she might not feel comfortable giving you her phone number. Leaving yours, it takes the pressure off and gives her the initiative. If her IL is above 50%, she will contact you. If it is 50% or below, you probably won't hear from her.