When you customize software, someone writes new code. When you configure software, you rely on the code as written, but change field names, tables, arrangements on the screen, and other elements of the software (See my post of May 23, 2007 about GE’s technology efforts, the disadvantages of customized software, and references cited.).
Customization is often expensive, lengthy, and problematic; configuration enables minor modifications within the pre-set limits of the package. Customization depends on the technical skills of the vendor and their willingness to depart from their package. Configuration depends on the flexibility built into the software but mostly on the willingness of the law department to tailor the as-is software as much as possible to its needs. My bias, I suppose it is obvious, is toward configuration and away from customization.