When calculating the Walk Potential of locations, one metric that's considered is parks with 10-minute walk from a location.
Should private parks be be included in the calculation?
I think it depends on how you plan to use it. The original use of Walk Potential was to aid city planners in finding the optimal places to fill in gaps in the sidewalk network. I don't expect building public sidewalks to private parks would be top priority.
However, if you are using the metric for a commercial real estate project, you want to count as a private park in a neighborhood as an interesting amenity.
I'll be updating default Walk Potential algorithm to not consider private parks, but I'll document how to include them in case people want to include them in their own calculations.
This question highlights the value of using an open source algorithm. You can see the details of the formula and tune it for your needs if need be.