Interesting memories ... IIRC: workstations were really what caused /dev/*mt* to stop being a standard name, so not screwing it down and using the -f option made sense. But for a long time, since it was less typing on the 11s and Vaxen, I would do:
tar cvb0 20 mumble...
However, once we moved to the world of networking, the -f option became important to me.
i.e. tar cvf - mumble | rmt hosts ...
Also, the DEC drives had better buffering. Large buffers became really important with streaming versions of 9-track and of course for the later QIC tapes. So blocking became even more important and I quit doing that function with tar itself and started to pipe tar through dd to do the blocking to get really large blocks (like 256K or 1M). Also, tools appeared like "double dd" (aka ddd(1)) program that originally used a two processes and pipe to coordinates the writes so that we could stream a Cipher drive on a 10Mhz 68K (Masscomp box).
[Note to Will - you might to google for the original ddd or talk to me offline, I bet I have it somewhere. Its an interesting program to analyze if you really want to get some insight on what you could do with UNIX even on a "slow" computer by today's standards and without a lot of today's fancy API's].
tjt rewrote dump(1) on RTU to use AST's and may have hacked dd too (I've lost that version I fear). In the mid, 80's I rewrote ddd to use threads once kernel support for threading became available and I still use that version today when I mess with tapes (which I do less and less, but have been known to do when trying to recover old tapes).
Clem