PL/Pgsql or PL/Python?

Hello,

I was wondering whether it is worth for me to learn PL/Pgsql, given the
support of Python in Postgresql. The latter (Python) is the only
programming language I've learned voluntarily in my whole life, i.e.
without being obliged to do so, you know. ;-)

So, what things can be done in PL/Pgsql which can't be done in PL/Python
(and vice-versa)? And, how do both compare in terms of runtime efficiency
(speed/memory)?

Apart from typical "ERP-like" work, the applications I am planning to use
Postgresql for involve storage and (numeric) processing of quite
significant amounts of (binary) measurement data. Specifically, "hacking"
long streams of binary data fed into a database in batch mode into
individual OPC-conform triplets, among others. So I thought the numeric
module and iterator feature in Python would be quite useful...

TIA,

Best regards

Wolfgang Keller