Should I reuse my private key?

I just tried to generate a new private key using:

ssh-keygen -t rsa

and it told me the file already existed and asked my permission to overwrite. I declined.

Is it okay to use one private/public key pair for different things? I'm not sure what the old one is doing, so I thought it best not to overwrite it.

I know I can create a new location for a new key pair but wanted to see if anyone know the best practice.

thanks