A self-report method is a data collection technique used in personality assessment where the information about the subject is provided by the subject itself. There are three types of self-report tests: Direct self-ratings, Indirect self-reports and Open-ended self-descriptions.

Self-reports are the most common assessment procedures for collecting data in psychology and psychological assessment. They can be obtained through questionnaires, inventories, or scales containing set of relevant verbal statements and a variety of response formats (true or false options, checklists, scaled responses, etc.). MMPI-2 and 16 Personality Factor Questionnaire are couple of famous self-Report Inventories.

Strengths

1. Efficiency: It is possible to administer large number of tests in relatively short space of time. Many self-report inventories can be completed very quickly, often in as little as 15 minutes. 
2. Broad coverage: Human beings can report on their private, unobservable, subjective world, their thoughts, and their emotions, as well as public observable events.
3. Multi-trait analysis: Multi-dimensional inventories allow measurement of multiple traits.
4. Inexpensive: It is an affordable option for researchers faced with tight budgets.
5. Reliability: Generally much more reliable and valid than projective tests. Scoring of the tests are standardized and based on norms that have been previously established.
6. Interpretability: Self-reports are communicated in the language common to the assessor and the respondent, therefore, easy to interpret and with better accuracy.
7. Information richness: No-one has better access to information about the respondent than the respondent himself.
8. Motivation to report: Whereas ratings of others may be done carelessly or superficially, people tend to put in more time and effort when reporting on their own personalities.
9. Causal Force: It engages the respondent's identity. In sum, the causal force of self-perceptions make them important to personality assessment in a rather different fashion from other indicators-reputation, for example (Hogan & Smither, 2001).
10. Easy to administer: Someone with little training can administer the test.

Weaknesses 

1. Susceptible to deception: Research has shown that people are able to exercise deception while taking self-report tests (Anastasi & Urbina, 1997).
2. Influence of social desirability: Responses may be swayed by desire for positive and negative impression management.
3. Acquiescence: Tendency of the subject to respond in the affirmative to all questions.
4. Impact of situational factors: Length of the question and tests, formulation of the question, type of answer and response requested, time pressure and subject’s characteristics impact responses.
5. Prone to biases: anchoring effects, primacy and recency effects, and consistency motivation impact self-report results.

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Human beings are the most important source of information about themselves; several assessment methods are, therefore, based on self-reports. They have several advantages, including ability to get reliable results in an easy, efficient and inexpensive manner. Their accuracy is threatened by several factors ranging from deliberate deception to unintentional errors and biases. However, it is commonly accepted that self-report questionnaires can be optimized through various strategies, and that their accuracy can be maximized.

Sources:
Encyclopedia of Applied Psychology (Click for eBook)
http://psychology.about.com/od/psychologicaltesting/f/self-report-inventory.htm
Handbook of Research Methods in Personality Psychology, Richard W. Robins, R. Chris Fraley and Robert F. Krueger (Click for eBook)