Describe will automatically show you the basic statistics of the all numeric columns like count,stddev, min , max etc. If you want a quick view of the numerric fields.

Summary allows you to explictly specify what you want to see in the output e.g. quartiles for distribution of data and standard deviation only. e.g. it can work on non-numeric columns also it can show you percentile etc with non-numeric fields whereas describe cannot do this.