The Art of Genjutsu: Illusionary Techniques.

[…] The greatest advantage, as well as the greatest disadvantage, of Genjutsu is its chakra consumption. While most Genjutsu don't require too much chakra in the sense of using and therefore wasting it, they require the caster to use a certain amount of their chakra to flow through their, and sometimes their victim's, bodies. The amount of chakra that is needed for this flow can't be used for anything else for as long as the technique is active, this being the main reason as for why only people with a certain amount of chakra are able to use the most powerful techniques.

If the caster releases their technique, the chakra used for this process becomes free once again and can be used as usual. Should the victim break the illusion though, all the chakra used for the energy flow will be wasted just as if you used it for another technique. […]

[…] Genjutsu, just as Ninjutsu, are ranked depending on the difficulty and the skill necessary to perform the technique as well as its strength. Both types of Jutsu share the same ranking system, ranging from D-rank at it's lowest to S-rank at it's highest.

Shinobi who specialized in Genjutsu more commonly use the terms low-level, mid-level, and high-level when they talk about their techniques:

Low-level techniques (generally Jutsu who rank from D-rank to C-rank) describe a Genjutsu in which the quality of the illusion isn't good enough to be unnoticeable and easier to break than mid-level or high-level techniques. The person that is victim to such an illusion can break free by simply disrupting their own chakra flow. Illusions of this level are generally used by shinobi who outnumber their enemies because victims of such illusions stay motionless until they break free. This way, they're easy targets for one's comrades. Caster of low-level Genjutsu are in general unable to move around themselves for as long as they use the technique, which is why they also require to be defended by comrades while executing the technique.

This is the most common type of illusion used by shinobi, as most don't have the chakra control to learn the other types or just don't bother to learn them. Techniques of this level can be used by forming the hand seal for Ram.[...]

[…] Mid-level techniques (generally Jutsu who rank from C-rank to B-rank) describe a Genjutsu that make it hard for the victim to notice the technique and often stay captured in the illusion until they get killed. Victims of such illusions move according to what they see inside the Genjutsu, which means the caster can make the victim attack their comrades without them even realizing it.

They either need someone else to disrupt their chakra flow for them or experience some sort of pain, for example by stabbing themselves with a kunai, to break free. Furthermore, most casters aren't able to move around themselves as they need to concentrate to keep the illusion going. Experienced users can maintain some mobility.

Every large-scale Genjutsu, which affects an entire area instead of a single person, is at least a mid-level technique.

Only a small number of Shinobi bother to learn mid-level Genjutsu as they prefer Ninjutsu because of their more visible effects. Techniques of this level can be used without hand seals if the caster's chakra control is good enough. However, diverse hand seals can be used if this control is lacking.[...]

[…] High-level techniques (generally Jutsu who rank from B-rank to A-rank) describe a Genjutsu during which it's nearly impossible for the victim to notice the illusion. To break free from it, the victim does not only need to realize their situation but also needs to possess excellent chakra control. People with such good control are almost as rare as people who able to use high-level illusions in the first place. The only other way to escape is being rescued by one's comrades.

One main difference compared to low-level and mid-level techniques is the additional benefit for the wielder of being able to move around freely once their victim is captured inside the illusion.

Whether the victim stays motionless or not while being inside the illusion depends on the will of the caster.[...]

[…] While there is no S-rank Genjutsu known to the wider public, such a technique may be in the possession of some clans.[...]

[…] If you fight against certain Kekkei Genkai users, like members of the Uchiha Clan and their famed Sharingan, remember that these rules don't apply to them in the same way as they do to you (for a complete list of all known bloodlines limits with ties to Genjutsu, turn to page 128). […]