Grooming is not part of the scrum process but it can be considered a very important part during the whole scrum framework. An effective grooming can help to plan the next sprint, to group user stories by epics or themes and define a new priority for user stories during a sprint. So the backlog can change rapidly.
IMPROVING THE BACKLOG
The product owner can receive feedback from the team itself. He can gather more useful information about the current sprint, technical informations about the user stories on next sprint and redefine not only the priority but even epics. He can add more "technical" user stories or analysis user stories to help to solve complex problems and keep the focus factor constant. The aim is to gain time and have less difficults to deal with problems. And sure when you split a user story in two or more parts, you will be more satisfied when you solve problems and get more story points :)
TECHNICAL USER STORIES
We use to call "technical" user stories the stories where developers can do the most important tasks. Generally we have seen UX and content can be always considered especially when you are working with web application and you want the UX is the best you can give to your customers. But the work of a web developer is reduced.
ANALYSIS USER STORIES
The analysis stories are user stories we use to analyse data and create some documentation and prepare ourself for the next story. If we are more confident and we know better how to work, we can make a planning defining the story point without big mistakes. So even if the main user story will remain the same, we have split the story into analysis and the story itself. I'll tell you this is a working method to go well solving problems because it worked each time we weren't confident or we had some suspicious impediment or some info to gather before plan the user story. That's doesn't mean the story was not ready, and doesn't mean the team was not ready to solve all problems planning more or less story points. We've made the same job with the effective time we needed and we earned a lot of time!
DEDICATE TIME FOR THE GROOMING
Do you think we dedicate too much time for the grooming? We've split the grooming for developers, UX (web designer and content) and a general grooming for the whole. Only 1 hour 1 or 2 times per week. That is sufficient to make a real effective grooming for a team with more than 5 people!