Identify trends and patterns
Notes are useful in analyzing which trading strategies work, and which are worth reconsidering. Make notes on the charts you're using, the patterns you're watching, and how certain events impact your trade. Over time, you'll be able to recognize the underlying mistakes costing you money. Writing things down prevents you from repeating the same mistakes.
Improve your trading techniques
Having a detailed record of past trades allows traders to better understand their strengths and weaknesses. Jotting down how you feel is a good idea - it can help you realize whether you're making emotionally driven decisions that ultimately hurt your trade. A trading journal gives you important insight about who you are as a trader, and what you should focus to polish up your skills.
Monitor your progress
The longer you trade, the more difficult it becomes to keep your progress in perspective. Writing down your goals makes it easier for you to remember what you want to accomplish. It also serves as a source of motivation. A trading journal allows you to keep tabs on your growth as a trader, helping you become more confident.