There are numerous reasons you may need to use multiple SSH keys for accessing GitHub and BitBucket
You may use the same computer for work and personal development and need to separate your work.
When acting as a consultant, it is common to have multiple GitHub and/or BitBucket accounts depending on which client you may be working for.
You may have different projects you're working on where you would like to segregate your access.
The only way I've succeeded so far is to employ SSH.
Assuming you are new to this like me, first I'd like to share with you that your Mac has a SSH config file in a .ssh directory. The config file is where you draw relations of your SSH keys to each GitHub (or Bitbucket) account, and all your SSH keys generated are saved into .ssh directory by default. You can navigate to it by running cd ~/.ssh within your terminal, open the config file with any editor, and it should look something like this:
Host * AddKeysToAgent yes
> UseKeyChain yes
I have two Github accounts: oanhnn (personal) and superman (for work). I want to use both accounts on same computer (without typing password everytime, when doing git push or pull).
Use ssh keys and define host aliases in ssh config file (each alias for an account).