For this distinctive style of play, recharge time reducing skills and activation time reducing skills are valuable for PvP (e.g., Soul Twisting, Ritual Lord and Serpent's Quickness). It is a very versatile strategy that can be used in many different places as a very powerful solo build as well as a strong part of a party.
They are typically primary Ritualists called Spirit Lords with builds designed to place three (or more) spirits as the core foundation of their builds; a key vulnerability fact that can be exploited by enemies capable of countering spirits. They create spirits and keep them alive, or frequently resummon and quickly dispose of them, depending on their role.
Ritualists' use these spirits to tactically secure essential areas and are often quickly place many spirits within range of some strategic capture or choke point in order to either aid allies or hinder enemies. This allows the team to focus on offensive measures, while the spirits harass or slow attackers using spirits like Pain, Shadowsong, or Bloodsong, which are a sort of defensive barrier at the same time.
Ritualists using Signet of Spirits are currently the most common Spirit Lords. When deciding to take several Spirit Lords in the same team, take special care to avoid having two spirits of the same name within range to each other and consider changing your builds accordingly.
Many other professions are also able to Spirit Spam quite well; Rangers can summon at low energy cost because of Expertise, Elementalists can summon high energy requiring spirits because of Energy Storage, and Necromancers are rarely concerned due to Soul Reaping's effect. However, primary Ritualists have access to Spawning Power and can also add runes to make their spirits much more effective both as indirect damage-reduction and direct-damage dealers.
Since the June 2009 update and the February 2010 update many binding rituals and spirit-related skills in PvE received buffs allowing for faster spirit creation, increased strength and shorter recharge times across the Ritualist attributes.