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Rigid foam board insulation works well for walls, especially basement and exterior walls, because they're moisture-resistant. They can offer adequate insulation, depending on your climate zone. But in colder climates, you might need to stack them. Rigid foam insulation is typically found in basements between the studs or along a concrete wall. Rigid foam insulation also gets used on a home's exterior behind the siding.

Yes, rigid foam is a good insulator since it can reduce air infiltration and thermal bridging, which occurs if there's an easier path for hot air to travel. Rigid foam also can have a higher R-value than conventional fiberglass batt insulation and doesn't carry high spray foam insulation costs.

You can use rigid foam insulation in various spaces, but it typically gets installed in basements, crawl spaces, and exterior walls. You can install rigid foam insulation in attics, but when it does, the attic typically gets finished since rigid foam needs drywall installed behind it, raising attic insulation costs. Depending on your climate zone and building codes, you might need to stack boards on rigid foam insulation because the R-value doesn't usually exceed an R-15 level. 

The International Association of Certified Home Inspectors has said foam board insulation can last up to 100 years if properly installed. Some insulation materials can suffer from water damage or start to sag over many years, thus reducing their insulating ability. Foam boards shouldn't suffer from sagging but have the potential to get damaged. Any broken pieces of foam board can reduce its insulating effectiveness.