You have 3 consolidation methods, depending on which level you with to enter validated work.
If you have
Project1
Phase1.1
Activity1.1.1
Activity 1.1.2
Phase1.2
Activity1.2.1
Activity1.2.2
You may want to define validated work only on phase level. If consolidation is automatic, 0 values on activity level would erase Phase value.
Imagine you define
validate on Project1=40
validate on Phase1.1=10
validate on Phase1.2=20
With consolidation = NEVER, you would get
Project1 =>40
Phase1.1 => 10
Activity1.1.1 => 0 (not defined)
Activity 1.1.2 => 0 (not defined)
Phase1.2 => 20
Activity1.2.1 => 0 (not defined)
Activity1.2.2 => 0 (not defined)
=> Project value is not consolidated as sum of Phases
With consolidation = ALWAYS, you would get
Project1 =>0
Phase1.1 => 0
Activity1.1.1 => 0 (not defined)
Activity 1.1.2 => 0 (not defined)
Phase1.2 => 0
Activity1.2.1 => 0 (not defined)
Activity1.2.2 => 0 (not defined)
=> zero values at lowest levels are cnsolidate up to project
With consolidation = ONLY IF SET, you would get
Project1 => 30
Phase1.1 => 10
Activity1.1.1 => 0 (not defined)
Activity 1.1.2 => 0 (not defined)
Phase1.2 => 20
Activity1.2.1 => 0 (not defined)
Activity1.2.2 => 0 (not defined)
=> zero values at lowest levels do not overwrite non zero values at phase level
=> non zero values on phase level are consolidated on Project level : value is updated to sum of phases
=> This is my choice for consolidation