So, how often do you mkdir a directory without cd’ing into right after? Sure, it does happen, but not very often. Which is why I have the following mkcd command in my .zshrc:

mkcd () {
    mkdir -p "${1}"
    cd "${1}"
}

I was reminded of this again when setting up a new machine (in the few minutes before I had cloned my dotfiles repository). So, if you want to save some seconds of cd’ing into newly created directories, add the code above to your .bashrc/.zshrc and alias mkdir to echo "no. use 'mkcd'." for the first few days.