When importing leads the match option can be selected. Matching on email address will prevent duplicates. Additionally, when you convert a lead you are presented with a screen asking which objects (Person, Organisation, Opportunity) you wish to create. If a similar Person or Organisation already exists they will be displayed in the “duplicate” list.
Having said that, we are aware of the requirement to merge records. Typos, and the human factor will always have potential to allow duplicates to be created. When this happens a merge would be very handy to merge notes, emails etc onto one record.
We’ll scope this issue and continue to gather requirements and examples (#2537)