Solaris

Though the root file system goes to 1st slice which is s0 by default and its standard which is followed, however it’s not mandatory. You can install the OS in any of the slice excluding slice s2 as this slice represents the entire disk.

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Swap is needed as its virtual memory, rest you can keep in same slice, however its imported to note that in case you have log which keep growing faster the its always wise to keep it in separate slice not to chock your root file system. In case you have lot of installing going then its equally important to keep /usr in different slice.

All above are the standard practice, however not a compulsion. Being an admin by seeing the requirement and the build document you have to take decision as what best suites your environment