Actual Work & Actual Work Protected - Why?

[Matt]

Can somebody explain why there is a need to have 2 fields that represent the
actual work performed by resources? I work in a managed time period setting
and do not see what the advantage is of having an actual work field that
users can edit directly in the plan. I understand that when the plan is
synced to protected actuals actual work should equal actual work protected
again - but why let it get out of sync in the first place?

Thanks,

Matt