For soft serve ice cream machines with refrigerated mix tanks, as well as those with overnight storage mode, it is generally safe to leave the soft serve ice cream mix inside the machine overnight and use it again the next day. The refrigerated mix tanks helps to keep the mix at a safe temperature to prevent bacterial growth.

Similarly, for soft serve machines with a pasteurization function, it is also safe to leave the mix inside the machine overnight. The pasteurization process helps to kill any harmful bacteria that may have developed in the mix.

However, it is important to follow proper cleaning and sanitization procedures before and after storing the mix overnight to ensure food safety. Regular maintenance and cleaning of the soft serve machine are essential to prevent contamination and ensure the quality of the ice cream.

In conclusion, it is generally safe to leave soft serve ice cream mix inside the machine overnight and use it again the next day, as long as the machine has the necessary features for safe storage and proper cleaning procedures are followed.