The SharePoint item REST API has its limits. One (or two in this case) of these limits is about returning values for fields you specified, more in particular when using lookup- or managed metadata fields. The problem with the lookup field occurs when it references a list from another web.
A project I was working involved retrieving all external / guest users that have been added to Office 365 and especially to Office 365 Groups. As it had to build in to an Office 365 application I choose to work with the Microsoft Graph. First thing I did was retrieving all users with the standard API call:
Some time ago I was testing out the Google Visualization API with SharePoint 2010 Rest functionality. The Google Visualization API is very handy if you want to visualize your data. My intention was to create a pie chart to visualise the task statuses. The data was consumed from the SharePoint 2010 REST service with the help of jQuery.