This will allow users to not have to parse PBS_NODEFILE or job attributes to know which nodes they want to keep or release.
Suppose I get a job by asking for:
qsub -l select=15:model=abc:mpiprocs=5+4:model=abc:bigmem=true:mpiprocs=1+30:model=def:mpiprocs=32
Then I want to release most of the nodes, but keep 2 of the non-bigmem abc nodes, and 2 of the bigmem abc nodes. It'd be much easier for the user to provide a new select statement:
pbs_release_nodes -k select=2:model=abc:mpiprocs=5+2:model=abc:bigmem=true:mpiprocs=1
than to have to determine via PBS_NODEFILE/qstat/pbsnodes which nodes have to be individually specified to pare back the job to that smaller select statement description.