Let's say you're implementing a REST API in Rails. When serving a collection, you might want to only include a few attributes:
/people
But when serving a single resource, you want to include all the attributes:
/people/1
I don't see how to do that using ActiveModel::Serializers, since the examples all use the pattern of defining one serializer per model (with a standard naming convention) and having AMS automatically use the right one in the controller when you do:
render json: @people
or:
render json: @person
To avoid mixing view concerns into your models (via serialized variations), use the view to render your JSON for each action, much like we do for HTML.
jbuilder & rabl both fill this data templating need quite nicely.
Update 2013-12-16: The ActiveModelSerializers library does support defining multiple serializers for one model, as @phaedryx answered later, by using custom serializers.