multipleenumerations.cs

public IEnumerable<YourType> GetYourTypes()
{
  yield return GetElement();
  foreach(var el in GetOtherElements())
    yield return el;
}

var types = GetYourTypes();

if(!types.Any()) // possible multiple enumerations of enumerable
// Do something

foreach(var type in types) // possible multiple enumerations of enumerable
// Do something


vs


var types = GetYourTypes.ToList();
if(!types.Any()) 
// Do something

foreach(var type in types)
// Do something