Mo Williams is a great point guard and would be a starter for at least 10 to 12 teams in the NBA—but not for the Clippers.
Williams is behind both Chris Paul and Chauncey Billups, two guards that are better fit for the Clippers than Williams is. Keeping Williams on the bench is good for depth at the point guard position, but it is not necessary when both Randy Foye and Eric Bledsoe are also back up guards who could be starters on other teams—just ask the Lakers.
The ideal trade would be the Clippers sending Mo Williams to the Utah Jazz for Paul Millsap.
Millsap would provide the Clippers with more depth down low—which is something they need because Brian Cook is only a threat to himself. Millsap would also be more than helpful when Blake Griffin or DeAndre Jordan are on the bench getting some rest.
Disclaimer: This trade is only speculated, there has not been talk between the Jazz and Clippers for this move.