When specifying an output file without specifying a logfile, the output file will be truncated anyway.
How exactly is using
ddrescue -t /dev/devicename outfile functionally different from ordinarily specifying an output file?
The only way
ddrescue -t (or
ddrescue --truncate) is different is that when trying to specify a logfile, ddrescue responsds with:
ddrescue: Outfile truncation and logfile input are incompatible.