Key things it appears to do:

• Browse other After Effects project files directly from inside AE

• Import only the compositions you need

• Avoid importing entire project structures unnecessarily

• Speed up template/library workflows for motion designers

• Help reuse animation setups across projects

It’s especially useful if you:

• maintain a reusable animation library,

• work with many client projects,

• frequently copy precomps between projects,

• or build modular motion graphics systems.

The current listed price on aescripts is around $29 USD, with periodic discounts.  

Related tools/workflows people often compare with it:

• LayerStash for saving reusable layers/setups

• True Comp Duplicator for duplicating comp hierarchies

• compCode for reusable project structures