Writing in first person is generally used for recording personal thoughts and feelings when writing a personal diary or keeping a journal. Memoirs, personal journals and diaries are types of biographical writing which do need to be written in the first person, clearly indicating what “I thought”, what “we did”, describing how something made an impact on “me” or how “our lives” were changed.

Providing an eye witness account is another way of describing an experience that allows readers to share immediate impressions and emotions felt at the time. This is not so effective in a third person report, which could only state that people who were there at the time appeared to be angry, shocked, frightened or having a good time.

Product reviews can be written as personal testimonials, if the writer is required to be open and honest when giving a personal response. Constructive criticism and praise will be more direct and effective when written in first person. A personal opinion can be more acceptable than a general rebuke or a vague commendation.

Read more about keeping a journal:
Journaling Tips  
How to motivate yourself by writing a journal entry about a day that hasn't started
I shall be posting more writing tips, and information about ways of writing, on my new blog: Writing Guidelines