Custom softwares are specially developed for some specific organization or other user. Since custom software is developed for a single customer it can accommodate that customer's particular preferences and expectations
Custom software will generally produce the most efficient system as it is can provide support for the specific needs of the business, which might not be available in an off-the-shelf solution and will provide greater efficiency or better customer service.
Given a suitable approach to development, such as DSDM, custom software will also produce the best or most well-targeted service improvement. Businesses can tailor the software to what their customers want instead of having to choose a package that caters for a generic market.