Another reason to use $state.params
is for non-URL based state, which (to my mind) is woefully underdocumented and very powerful.
I just discovered this while googling about how to pass state without having to expose it in the URL and answered a question elsewhere on SO.
Basically, it allows this sort of syntax:
<a ui-sref="toState(thingy)" class="list-group-item" ng-repeat="thingy in thingies">{{ thingy.referer }}</a>