Advantages of using Item Bucket? 

Applicable for Sitecore 7.0 and above.

An item bucket addresses the problem of managing large numbers of items within the content tree,
retrieving them, and working with them in a speedy and efficient manner. To decide if you should turn
an item into an item bucket, and in-turn, hide all its descendants, you must ask yourself if you care
about the structure of the data that is stored in the item bucket.

For example, if you have items within the content tree that contain a large number of sub items such
as products, media, or tags, it may be an advantage to turn these items into item buckets and thereby
remove the need for hierarchically managing the content.

Important
Note that a connection between two or more items does not necessarily need to be hierarchically.
Then when you want to work with a particular item placed in an item bucket, you can search for it and
open it. The advanced Sitecore search functionality allows you to search among all items in Sitecore
using for example free text, search filters, or facets, that makes it easier for you to find exactly what
you need.

Ref : http://sdn.sitecore.net/upload/sitecore7/72/developer's_guide_to_item_buckets_and%20search_sc72_a4.pdf