What is the difference between InMemory and TempDB temporary tables?

InMemory and TempDB are both temporary, but they behave differently.

InMemory

• Starts in application memory.
• Can spill to disk as it grows.
• Works well for smaller temporary datasets.

TempDB

• Uses SQL temporary storage.
• Supports SQL-side joins and set-based processing better.
• Is usually the better fit for larger datasets and many SSRS/reporting scenarios.

I normally reach for TempDB when the dataset is not tiny or when I know I will be joining/querying the temp data heavily.