Docstring and perf note
Docstring and perf note

dask/dask,clarkfitzg/dask,clarkfitzg/dask,mikegraham/dask,vikhyat/dask,ContinuumIO/dask,dask/dask,ssanderson/dask,blaze/dask,jcrist/dask,PhE/dask,chrisbarber/dask,jakirkham/dask,mrocklin/dask,mraspaud/dask,blaze/dask,cowlicks/dask,mrocklin/dask,cpcloud/dask,mraspaud/dask,jakirkham/dask,vikhyat/dask,ssanderson/dask,gameduell/dask,pombredanne/dask,PhE/dask,jcrist/dask,pombredanne/dask,ContinuumIO/dask