|esriSelectionTypeHybrid||3||Snapshot if small, else an ID Set.|
Depending on the number of rows or features selected this option lets you define if the SelectionSet will store only IDs or a set of instantiated rows in memory.
The selection is always based on a persistent set of OIDs (e.g. logfiles for ArcSDE)
The selection is always based on a set of in-memory rows (e.g. no logfile just in-memory IRow(s))
The selection itself decides how to manage its representation (e.g. it may morph between IDSet and Snapshot)