must run in a Shell using SH

As instructed in a Readme for an Oracle patch, the instruction is to explicitally use a given command:

sh command.sh

Now, the script itself has a shebang to SH, first line states : #!/bin/sh

My question is this : how would it behave differently, if I call it like this:

command.sh

The Shell I'm in would probably be a Bash shell, or a Bourne Shell even, but I assume all of that is not relevant even. I don't understand why a script should be called like that, IF the script itself contains a command to force using a given shell in the first place. And, the script and the instructions come from the same vendor.