Rosemary is definitely the first herb you want in your magical cabinet. The reason, you may ask, is because you can substitute this herb in to your magical practices. For example you don't have sage, no problem use Rosemary. Got no Thyme? replace it with Rosemary.

 As a cleansing and purifying agent in magic, Rosemary is one of the more important herbs. Rosemary was associated with love, friendship. It is one of the oldest incenses... so what's not to love?

Rosemary comes from the word Rosmarinus which is Latin meaning "dew of the sea" 

Rosemary was used to ward off evil spirits and nightmares. 

An old saying goes... "Where Rosemary flourishes, the Woman rule" and in England it was believed that Rosemary could not grow in the garden of the home unless the mistress was the master!

Rosemary is useful for bathing before rituals, and for making sacred herbal water for ritual cleansing, blessing and purification. 

Bathing in Rosemary will enhance your memory and will make you more memorable to those you meet throughout the day. 

Rosemary oil rubbed into the ends of hair will also help reduce split ends and even help baldness.
As a symbol of fidelity, a Rosemary bush, or crafts made of Rosemary are suitable wedding gifts.
Handfasting (Pagan weddings) couples may wear Rosemary crowns to bring babies very soon.
In hedge-witchery, Rosemary is used as a garden-friendly substitute for precious, exotic Frankincense, and smells as divine.
Rosemary is burned to purify a room or ritual space before magickal workings.
A Rosemary bush in the garden is supposed to attract elves and repel thieves.
Cleanse and consecrate athames, wands, and crystals with Rosemary oil.
A married woman may keep a sachet of Rosemary near the entrance of her home (or under her bed) to ensure a faithful and obedient partner.
Rosemary was also used in sachet for safe passage over water.
Rosemary has also been used as incense, along with juniper for aiding in recuperation.
It is advisable against use in pregnancy as it has been linked to miscarriage. The oil especially is a diuretic and uterine stimulant. It is better to be safe than sorry when pregnant and be cautious.
I will post spells which may include Rosemary later on, but I would advise you to have Rosemary plants and essential oil. Its definitely worth it and the aroma is lush.