If you have an extension which maps a type A to another type B and you have an enumerable of type A which you want to turn into an enumerable of type B, should you prefer
.Select(x => x.ToB())
.Select(x => x.ToB())
or
.Select(Extensions.ToB)
.Select(Extensions.ToB)
? The first I assume allocates an extra unnecessary lambda which the second doesn't?