Why is ToWorldSpace required in basic CFrame rotation?

Hello all.

I'm a beginner scripter and have just started touching on CFrames today. I've been using the Roblox Wiki as my guide and so far I've been keeping up with what's going on.

I've just read this page here (Understanding CFrames) and done all the excercises twice. I understand all except one thing; Dynamic CFrame Orientation (as the Wiki puts it), or more specifically, the ToWorldSpace CFrame function when used in simple rotation.

In this example, the Wiki provides you with this code which is supposed to point the front face of the red cube towards the blue cube, and then rotate the red cube so its top face is pointing towards the blue cube:

local redBlock = game.Workspace.RedBlock
local blueCube = game.Workspace.BlueCube

-- Create a Vector3 for the target position
local targetPosition = blueCube.Position

-- Point the red block's front surface at 'targetPosition'
redBlock.CFrame = CFrame.new(redBlock.Position, targetPosition)

-- Rotate red block's CFrame relative to itself so that its top surface (not front) points toward the target
local rotatedCFrame = CFrame.Angles(math.rad(-90), 0, 0)
redBlock.CFrame = redBlock.CFrame:ToWorldSpace(rotatedCFrame)

Everything here makes sense to me, except for line 12:

redBlock.CFrame = redBlock.CFrame:ToWorldSpace(rotatedCFrame)

My thoughts were that it would be something like this:

redBlock.CFrame = CFrame.new(rotatedCFrame)

I have of course tried this, and as I expected, it didn't work. However, in the original code (which works), I don't see why ToWorldSpace is required if you aren't using relative rotation (because you are rotating the red cube in the last 2 lines, nothing to do with the blue one).

So to summarise, I don't understand why you're using relative rotation for a rotation which relies only on itself. I thought relative rotation was rotating something relative to another thing.

Thank you in advance for you answer/help.