Request for explaination - Functions - Loops in VBA

This is in Excel.

The following piece of code works perfect if all I want to do is select every cell on each page 1 at a time.

However if the line below is activated (un-comment) then on the first pass (using F8), it goes right to the biginning of the function. (once hitting the line below)

'Cells(RCI, CCI).Value = Trim(Cells(RCI, CCI).Value)


Code is as follows:

Function Trim()
Worksheets(1).Select
SC = ThisWorkbook.Sheets.Count
SCI = 1
    For SCI = 1 To SC
        Worksheets(SCI).Select
        RC = Range("A1").CurrentRegion.Rows.Count
        cc = Range("A1").CurrentRegion.Columns.Count
            For RCI = 2 To RC     'loops through rows
                For CCI = 1 To cc ' Loops through columns
                    Cells(RCI, CCI).Select
                    'Cells(RCI, CCI).Value = Trim(Cells(RCI, CCI).Value)
                Next CCI
            Next RCI
   Next SCI
End Function