Advantages:
- Resist/protest unlawful/unfair taxes/government
- Prevent privacy intrusions (financial records) from governments/banks/corporations
- Counter-economic force

Disadvantages:
- Criminal usage (including money laundering)
- No means of refunds or fraud insurance

Which is more important:
The advantages will always be more important as long as there are more regular users than criminal users and there are no better methods for a user to gain the advantages.