Do you need separate API's per plugin or computer?

Greetings. I may have created a future problem. I think I used an API key that I obtained for one plugin in the setup of another and I'm confused as to where, exactly I made the error. Is this of major consequence? If I did make things hinky, will I get an appropriate error message at some point? Might one API key be universal and all the others I have signed up for are redundant? I do not know. Please - - enlighten me and allay my fears. Cheers. - Frank