I think you'll quickly find another benefit of journalling: It forces you to justify your decisions. Even if you only write for yourself, many ideas "sound smart" in your head, but don't seem all that bright when they've been put in writing and you re-read them.
You also get invaluable documentation of justifications for what you do.
And the effect multiplies when you decide to publish it.
I keep sporadically working on a series about writing a compiler in Ruby, which morphed into writing a Ruby compiler in Ruby, and it's a slow going slog (I just ended a two year "break"), and writing about it quickly started changing my approach. It's like when your maths teacher insist you show your working rather than just giving the results - you can't skip steps just because you know (or think you know) how to go straight from A to B any more. Of course when writing a journal, nobody is forcing you to not take shortcuts, but I find I am more likely to be disciplined about verifying assumptions an testing changes anyway.
You also get invaluable documentation of justifications for what you do.
And the effect multiplies when you decide to publish it.
I keep sporadically working on a series about writing a compiler in Ruby, which morphed into writing a Ruby compiler in Ruby, and it's a slow going slog (I just ended a two year "break"), and writing about it quickly started changing my approach. It's like when your maths teacher insist you show your working rather than just giving the results - you can't skip steps just because you know (or think you know) how to go straight from A to B any more. Of course when writing a journal, nobody is forcing you to not take shortcuts, but I find I am more likely to be disciplined about verifying assumptions an testing changes anyway.