This is a trick to running commands that you don’t want to be saved in your history.
You may want to run a command that isn’t stored in your history. You can do this with a preceding space.
# no preceding space
someCmd --key ABC123
history
# 98 ...
# 99 someCmd --key ABC123
# with preceding space
anotherCmd --key ABC123
cd ~
# notice `anotherCmd` is missing
history
# 98 ...
# 99 someCmd --key ABC123
# 100 cd ~
A common scenario may be when using sensitive values a single time (i.e. where you don’t want to take the time to set environment variables).