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The response modification factor R is in the denominator of the equation 12.8-2 for the seismic response coefficient CS used to calculate base shear, so that a high value leads to lower base shear.
The default response modification factors from ASCE-7 Table 12.2-1 are
For bearing wall systems: Wood structural panels - 6.5; Other materials - 2.0
For building frame systems : Wood structural panels - 7.0; Other materials - 2.5
These are summarized for each material in Shearwalls in Seismic Provisions.
The program allows you to specify the R that appropriate to you building system based upon the sheathing materials employed. Different R values can be input for each force direction, because of the possibility of different sheathing present in one direction than in the other.
The default R value is the one for non-wood panels, because the default standard walls include non-wood panels. Upon generating loads, if the program detects the presence of non-plywood materials such as fiberboard, lumber siding, or gypsum in a particular direction, it warns you and offers to change the R value to the one corresponding to "all other materials". If you choose to use an R value for wood materials in the presence of non-wood materials, then the program automatically checks the Ignore non-wood materials in design design setting, so that the gypsum and fiberboard materials do not contribute to shear wall strength. Refer to the changes made for Service Release 8.1 for more details.
You can also manually disable the contribution of all non-wood-panels for seismic design in the Design Settings.