If any files begin with '-', the second version will just expand to '-filename' which rm will try to process as an option (possibly failing or creating undesired results). Using

  ./*

expands to

  ./-filename

which won't be picked up by option processing. Note: You can also do

  rm -rf -- *

to prevent option processing after the '--'.

edit: added a bunch of breaks to prevent the * from being converted to italics.

The former will gleefully delete all files/directories, even if there exists a directory entry named "-i", without asking.

The difference is in glob expansion: ./* keeps the prefix on every expanded item. As mentioned above, using any sort of path (relative or absolute) prefix when globbing will circumvent all the careful "-i" wards a superstitious sysadmin may have put in place.