Buffers increases the drive strength to your load (in the form of capacitance), therefore the transition (slope) from 0->1 or 1->0 will be faster.
However, it will also increase the latency because it's just another level of logic in your path.
Think of it like this. Before you insert the buffer, you have a little guy lifting the load and doing it slowly. After inserting the buffer, you have a strong guy lifting the same load and doing it much faster.
- Hung