DAX is very powerful but it could entail a steep learning curve for novice users. Power BI Desktop has started on the road of delivering pre-packaged calculations. The first one is Percent of Grand Total. Once you add a measure to the Values zone, you can expand the measure drop-down and click Quick Calc. This is similar to how you would pick one of the default aggregation functions.
Interestingly, Power BI Desktop doesn’t add a new calculation when the Quick Calc feature is used. Instead, it probably creates an implicit DAX measure and you can’t see the formula. The original measure is renamed to %GT <original measure name>.
Prepackaged calculations are a frequently requested Power BI feature. Expect additional quick calculations to light up soon. As a recommendation for improvement, I think that it would be nice to be able to see the DAX formula behind the quick calc.