Multiple sgroups are used to simplify the depiction of chemical structures that contain the same collection of atoms and bonds multiple times like the Chloride in the following example of calcium Chloride
If you go into the details of [Cl-]2 you find out that two Cl- atoms are exactly overlapping so that only one is perceived while the index of the brackets reflects the number of overlaying levels. Therefore the left and right presentation of calcium chloride are identical except that the Sgroup brackets simplify the depiction. Analogously you find 100 polyethelene glycol units overlaying in the following example
Accordingly you receive the formula C200H402O101 and the molweight 4423 Dalton for this structure.