Codification could help make the sharīʿa more relevant to 'modern' issues, such as adapting to the growth of the global Islamic finance industry; the Saudi legal system has recently come under fire numerous times for alleged human rights violations.
Overhauling the justice system could help relieve the strain on currently overburdened courts, in part by establishing new criminal, family, traffic, etc. courts. New, better-trained judges would help make trials more fair, consistent, transparent and help establish consensus in rulings on important issues.
Of course, there is significant resistance to change within the Kingdom. Codification risks interfering with the independence of judges, for example.
Frank Vogel's Islamic Law and Legal System: Studies of Saudi Arabia (2000) is a substantive study on the legal system in Saudi Arabia; Vogel spent five years there conducting research (1982-1987). (he retired from Harvard Law School in 2007.)
As Vogel makes clear, the debate on codification is nothing new and has long been perceived as threatening.
As we have amply seen, codification not only runs afoul of a long-standing allocation of constitutional powers that makes the ʿūlamāʾ the legislators in private law and criminal law matters. It also offers offense to the deeply related notion that Islamic law is microcosmic in substance and application, a notion cherished by Saudi ʿūlamāʾ and by other Saudis, ruler and ruled.
However, as Vogel points out, there are historical examples which suggest that the sharīʿa could be codified in Saudi Arabia without losing its "ultimate ethical, textual roots:"
In the past Islamic legal systems existed that were much more macrocosmic in their practice, and [...] nowadays theories exist that attempt to legitimate modern democratic or liberal constitutional models as fully Islamic. Such findings as these make clear that Islamic law itself is not unalterably opposed to codification, and that there are many possible ways by which the Saudi system could evolve to include codification or a close substitute for it.*