This exact keyword phrase gets a decent number of exact monthly searches on Google.
Advertisers (that use Google AdWords) pay up to $9.03 for a single click generated by the ad triggered by this exact keyword phrase.
If you are using Google AdWords this domain will improve your Ad Quality Score and therefore your CPC price will be lower and your ad will be better placed. The purchase of this domain is a one-time investment in a life-time marketing.
Many people search exactly for this keyword phrase (Pittsburgh CPA firm) instead of searching for some particular firm and whoever will own this domain will be highlighted among the competition.