If the necessary interocclusal space is not provided, long term sequelae will be:
Effects of increase in vertical dimension 

Discomfort: Increasing the vertical dimension alters the environment in which unconscious movements of muscles during chewing take place and until the original condition is restored, discomfort will result. The jarring effect of teeth coming into contact sooner than expected also causes discomfort.
Trauma: The sudden and frequent contacting of teeth causes trauma to the denture-bearing area, especially under the lower denture, where the area to resist pressure is less.
TMJ problem: The constant tooth contact will also affect the TMJ causing soreness and pain.
Bone resorption: The increased vertical height does not allow the muscles that close the mouth to complete their contraction. They will continue to exert force to overcome this obstruction and this will lead to resorption of supporting tissues.
Muscular fatigue: Due to the constant effort of the muscles to close the mouth, muscular fatigue will also occur.
Clicking of teeth: The premature contact of teeth sooner than what the individual is used to, will cause clicking of teeth.
Facial distortion: There will be an inability to close the lips, which will produce a strained expression and elongation of face.
Difficulty in swallowing and speech: The inability to close the lips will also cause difficulty in swallowing and speech.

Effects of decrease in vertical dimension

Inefficiency: The biting force exerted by the teeth in occlusion decreases which causes inefficient mastication.
Cheek biting: The loss of muscle tone and reduced vertical height causes the flabby cheeks to become trapped during mastication.
TMJ problem: The patient has to often protrude the mandible to occlude the teeth and this causes pain and clicking in the TMJ.
Facial distortion: The following effects are seen:
	
Nose appears closer to the chin
Loss of lip fullness
Loss of tonicity of muscles of facial expression
Face appears flabby
Patient appears older


Angular cheilitis: The corners of the mouth form deep folds, which are bathed in saliva. This becomes infected and sore.

Key Concept:
A lack of interocclusal space results in excess pressure on ridges continuously. As a result of which, ridge  resorption takes place.
Ref: Textbook of prosthodontics V Rangarajan Ed. 2nd
Clicking of dentures
Ridge resorption
Soreness of tissues
Problems with speech and mastication