pattern for saving newline-delimited json with python

With Python, I'm saving json documents onto separate lines like this:

from bson import json_util # pymongo

with open('test.json', 'ab') as f:
    for document in documents:
       f.write(json_util.dumps(document)+'\n')

and then reading like this:

with open('test.json') as f:
    for line in f:
        document = json_util.loads(line)

The ease and simplicity make me think that there must be a gotcha? Is this all there is to linejson, aka jsonlines?