Foursquare is a location based service that helps consumers find businesses around them and engage with them. Listing on foursquare is essential because they are used as a location database for thousands of services and your business will be invisible in these services unless you are listed on foursquare.
The popularity of this service on social media and on various traffic metrics. You should look at Moz Domain Authority and Alexa Rank and compare to other services to determine how popular this service is in comparison to other services.
Must List
This service is considered to be a Must List service because it provides significant opportunities for your business. These services often are heavily used by consumers or your data on this service is used by many other services and apps. Not having a presence will mean your business will not be listed in many places online.
Foursquare Tips
Online Presence
Claims made by Foursquare
Foursquare Features
Classified as a Location Based.
Having a presence is free.
Predominately delivered as an app (iOS, android, windows).