Um... you tell us?
First off, if you've already bought it, then you didn't pick the DAC option (which is part of the ordering process), so moot point.
If you have NOT already ordered it, and are considering the DAC option - OR, if you have ordered it and are considering buying a standalone DAC, such as the HeadRoom Micro DAC, then it depends on your source(s).
A DAC is a digital-analog converter. Do any of your sources have a digital out? For instance, a computer has USB (and sometimes optical) output. Many good CD players have optical or digital coax outputs. Etc. If none of your sources have digital outs, and you're not anticipating getting a source with digital out, then a DAC would be kind of pointless.
However, if any of your sources DO have digital outputs, then a DAC might be a good idea depending on the quality of your source. A multi-thousand dollar Marantz CD player might have a better DAC then the optional DAC found in the HeadRoom Desktop Amp. On the other hand, the Desktop's DAC will almost certainly be worlds better than any laptop computer DAC.
A DAC increases the versatility of your setup, and is usually better quality than many source built-in DACs. But it totally depends on what you need and want.