Always write for your Audience. The first consideration? Is this just for you, for your family and friends, or do you want the world to have access and buy it?
If you're writing just for you, anything goes. The main consideration is how to keep it private - and whether you want it to be discovered when you're gone! If you do expect it to be read by others eventually, you probably want to keep them in mind as you write.
If you're writing for family and friends, you can be somewhat relaxed about form and grammar - but you want it to be readable, so some editing is advisable. You also have to consider how your content will be perceived by them - and how that may change their perception of you. Will you damage relationships by sharing this?
If you're writing for the world, it's a lot more work. Even if you're thinking of it as a hobby, you need to meet professional standards of editing and format - as well as expectations particular to your genre - if you expect the world to buy your work.
So, before you begin: Who are you writing for?