I hardly ever use Insight because each message is placed in an individual file
with a name of the form (eight digits).CNM, and the 8 digits are cryptic. With
the heavy traffic on Arachne and herb lists, the number of files becomes huge.
Now hearing about lost clusters with Arachne, which we previously heard about
from Boanne (no longer on this list), and knowing FAT is not the sturdiest file
system, I would use Insight only for upload (SMTP), or download only when the
expected number of messages is very low. I sometimes use Insight to read a
message downloaded in raw-data form with another program such as the OS/2 port
of popclient. This begins to answer Bastiaan Edelman's question about how to
see the raw data of email messages.
I believe the .CNM files you get with Insight are the raw data, and on SMTP
upload, the .TBS files are raw data.