This hint may help some people:
I had two very large tables that I wanted to combine.
AppendAll.mbx couldn't work due to columns not matching.
After making the table structures match, copy & paste just tied up my PC for ever, and made the clipboard unavailable for anything else.
Solution: Use the Mapbasic window with a command similar to this, depending what columns are involved.
Insert Into DESTINATION_TABLE ( COL1, COL2, COL12) Select COL1, COL2, COL3 From EXTRA_DATA DropIndex Auto
-- This was near instantaneous.
- MapInfo 12 or 15.