A Linespacing of 1 means use the standard GDI+ linespace when a cell has more than one line. A linespace of 2 would mean double linespacing, and 0.5 would mean half linespacing. Normally linespacing in Excel is a little bigger than linespacing in GDI+, so you can use this property to fine tune what you need. This property doesn't alter the Excel file in any way. It is only used when rendering.
property TExcelFile.Linespacing: Double