The elements don't add metal to the layout, but in circuit simulation they include the electrical parasitic effect of the T-junction and step in width.
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The width values of MTEE and MSTEP are the width of the adjacent lines.
Agree with Volker that these values are important and are used to calculate the parasitic effect cause by each discontinuity but there is nothing to 'calculate', they just need to be set to the width of the attached MLIN at each pin. If any different value is used then the parasitic effects are not being modelled correctly.