Def Col, Jangpura etc. are residential areas. Most of the buildings have basements that have been converted into office spaces spacious enough to accommodate 5-10 people max. These areas are preferred by small chambers due to the proximity to HC, SC, Tribunals etc.
Coming to the second question, South-Central Delhi has very few commercial office spaces for accommodating 200-500 employees. Most of them are in CP/Barakhamba Road area but those buildings are old, about to collapse and mostly reserved for government offices. AZB, KCO etc. used to have their main NCR office in that area but have now shifted to Noida for bigger, spacious and fancier offices.
Why do disputes teams of big law firms (AZB, Cyril Amarchand) etc are working out of Noida office which is far away from all courts and tribunals.
Coming to the second question, South-Central Delhi has very few commercial office spaces for accommodating 200-500 employees. Most of them are in CP/Barakhamba Road area but those buildings are old, about to collapse and mostly reserved for government offices. AZB, KCO etc. used to have their main NCR office in that area but have now shifted to Noida for bigger, spacious and fancier offices.