Sponsorship of an individual for a work visa

I have a limited company client who has asked me about any implications in sponsoring an individual who wants to remain in the UK on a work visa.

The individual is a New Zealand citizen who has been working in the UK (not for my client) on a work visa for 2 years. The visa is soon to expire.

This is not something that I have any practical experience of so I will do a Google search. I just wondered if anyone had any experience of this and whether or not there may be any pitfalls or disadvantages.

Many thanks.