You may be able to see all diary entries for a certain month but you won't see a list of items related to a topic spanning many categories. As the number of items grows to 5k, 10k, 50k, and beyond, it becomes exponentially harder to find a set of relevant items; it's also harder to enter items in the tree structure because you have to choose the most important category among many possible ones. Full-text search helps but it will often produce a set of results that is too big or too small—it is particularly difficult to use search if you're looking for a set of items instead of just one item, and you won't be able to sort results as you may do with Tobu.

Tobu makes it easier to enter new items because you don't need to fit them in an existing organizational structure—you only need to describe them.

Tobu is meant to be an evolution of a tree-like outliner that lets you maintain multiple web-like connections between items as opposed to a single descending parent → children connection.

The only tricky part of using Tobu is knowing which tags will describe the items in a way that will be most helpful when you search and sort them. There are no definite rules here, it takes practice to get the hang of it.