The TRAP writer already buffers writes before emitting to file, but running gzip compression is also fairly costly (especially if you only do it a couple of bytes at a time). Thus, this injects another buffer that collects the emitted tuples in string form, and only triggers gzip compression once the buffer is full. In my local testing, this buffering was actually more beneficial than the one between gzip and file (likely because the gzip writer already emits data in chunks), but that one is still beneficial.
