What is the importance of disclosure in financial statement?

It is a mandatory part of financial statements according to IAS/IFRS

meaning you cannot call it financial statements unless it has all the disclosures.

Financial Statements consist of

1. Income Statement or Statement of Affairs
2. Balance Sheet or Statement of Financial Position
3. Cash flow statement
4. Statement for Changes in Equity
5. Notes or Disclosures

I don't know anything about it 

Disclosure helps in better understanding of financial statements.