In 20 words or fewer, explain why a slave owner might free his slaves in his will. Why not sooner?

When he dies he will have no need for slaves so he might let them go.

Legislation under the early Roman Empire put limits on the number of slaves that could be freed in wills (Lex Fufia Caninia, 2 BCE), which suggests that it had been widely used. Freeing slaves could serve the pragmatic interests of the owner