Menstrual blood is usually used in love spells, etc, because of where it comes from. Menstrual blood is also waste blood; it's blood that the female body naturally sheds. It doesn't take a sacrifice, doesn't take any effort to gain, etc, and so usually is only used in certain types of magic.
It's similar to getting a Christmas present: Do you want the gift that someone else was given first, but didn't like or do you want your own gift?
Menstural blood is used for a variety of things. Think of what it represents. Nourishment, protection, attraction, and creation.
Unless you really know what you are doing I would not suggest using blood in spells and rituals. In doing so, you create a direct link to yourself. This can be useful for some things. However it could be dangerous if used improperly.
Whenever using blood in a ritual, be careful. Use proper sanitary methods such as one would use drawing blood in a hospital. Also it is not always necessary to use large amounts. Just a drop should be enough for most workings. It was suggested to me, to use one of the finger prick things they use for blood sugar monitoring. This way you are not putting yourself in danger from a possible cut to a blood vessel.
I've only ever used blood magick once, and that was to make a pact with someone. We pricked our fingers so that we wouldn't bleed too much and so we could clean it out more efficiently. It's the only thing I ever use blood for (and really, how often do I go around making pacts with people?)