What are the situations in which creating a substitution would be appropriate?

Generally speaking, a Will with substitution is used by the testator in the following situations:

• He/she wishes to ensure a decent standard of living for the surviving spouse until the latter's death, and stipulate that the residue of his/her estate will then be passed on to his/her children or grandchildren, without the requirement that a neutral administrator act jointly with the surviving spouse;
• Upon a second marriage.