LookupTable data is stored in memory and is not written to disk. You would need to investigate the memory usage for your particular table to determine if it would have any adverse effects. Depending on what you want to do, you may find iterating your data in memory faster than attempting to do so in an automation. I doubt there would be much difference time-wise if you iterated the data as a DataTable within an automation than simply iterating it in Excel within an automation. Time savings would be much greater if you performed the iteration in a C# script, but you'd need to be versed in C# to do that effectively.