It's good to set expectation up front with each other, and a performance plan is one way to go about doing it. The downside to completely getting rid of a co-founder is:

1) They're likely going to take /some/ amount of equity with them (have a vesting plan!)

2) Getting rid of a co-founder before you reach critical mass will be detrimental to the business. If not, they probably weren't a good pick for co-founder.

That’s true. However in some cases it can be difficult to agree on the voting conditions with other founders. If you agree on voting, make sure that you describe the procedure of voting: who can start the voting event, who will prepare a result of the voting, what will be in case when votes for both variants are equal, etc. I think  we’ll prepare a separate article about it.

In the UK you can vote them out as a Director but it is difficult to get rid of them as shareholders.

Some co-founders simply let themselves get booted but still cash in at a later date without have actually accomplished anything.