YoY means year over year and MoM means month over month. These numbers can be used to account for seasonality. For example, in places that celebrate Christmas, editing activity decreases so it wouldn't be useful to compare December numbers with July numbers. Are these numbers useful at a glance or better left in the detail pages?
Topic on Talk:Wikistats 2.0 Design Project/RequestforFeedback/Round1/Site dashboard
Is it important to see both YoY and MoM changes?
I would say yes, these numbers are useful. But please tell what you compare MoM: a day or a month? If month, are months normalised (e.g. will March have a 11% increase over February for well-known reasons?)
Well, we can use whatever approach people find useful, but typically MoM compares the average of this month to the average of the previous month. This takes care of the normalizing issue you mention, which is a good point.
Then yes, both seem useful for me.
It depends on the statistic, for instance it doesn't make much sense to compare number of edits MoM.
Yes, it is important.