Tea leaves are of four grades - Whole Leaf, Broken Leaf, Fannings and Dust. Whole Leaf teas are the least oxidized, and have a better taste and aroma, and a higher degree of anti-oxidants that offer maximum health benefits.
Whole Leaf teas require a lot of space to unfurl/expand during brewing. Traditional filter paper teabags don’t allow this space. Therefore, these teas come either in the loose form, or in specially designed pyramid teabags that allow sufficient space for tea leaves to expand. Conventional teabags cannot have Whole Leaf or even Broken Leaf teas! These have Dust, or Fannings at the most!
Also, Whole Leaf teas release extracts slowly. Therefore, these are meant to be used 2-4 times depending upon the type of the tea and brewing temperature and time. In colder countries, people reuse tea leaves even on the next day. In India, it is recommended to reuse tea leaves over 6-8 hours.