A49 prevents building up too much density at some rather contrasty working films. I like it for aerial films like Rollei Retro 80 or Superpan 200.
It might explain why I got very good results with medium speed films like Plus-X but no so good with Tri-X. It might also comes form my development time... I need to investigate further. BTW, I use the ADOX version which should be pretty similar the the Calbe version.
"The problem with photography is that it only deals with appearances." Duane Michals
"A photograph is a secret of a secret. The more it tells you the less you know." Diane Arbus