I’m not sure the difference between a regular journal and a prayer journal - it just all runs together for me.
Here’s my experience: Last year before Lent, I had a journal that had some scripture verses here and there. I used a daily reflection booklet during Lent and often used the journal to further elaborate on the reflection. Prayer journal?? I don’t know.
After Lent was over, I continued to keep a journal. Often it is about prayer related topics. Sometimes I make notes on what the message in the homily was on that particular day. Sometimes when I am reading the Psalms from morning prayer or evening prayer, something will jump out at me, and I will write that down. Sometimes I just write about the events of the day. Sometimes it’s a vent. Sometimes not. Sometimes I will write my prayer in my journal. When I go to Adoration, I always take the journal, and will almost always write.
I have found it useful to go back and reread. Sometimes I can see progress. Sometimes I can answer my own questions. The last few times I have been to confession, I have spent the week or so before, rereading entries and using that as an examination of conscience. It has worked very well. It’s hard to wiggle out of a particular behavior or attitude when it’s right there in black and white.
The last time I went to confession, it was surprisingly difficult, and I used my journal to reflect on that experience. Sometimes it just helps me process things by writing.
I have also been known to write down things (names, phone numbers) that I don’t want to forget.
I can’t think of any cons, other than someone coming across your thoughts and not respecting your privacy.
I just use a small sized notebook - about 7x7 or so - for my journal and that works just fine.
Give it a try?