A couple are living outside the UK, one is a british citizen by descent, the other is not, and they wish to come here to live.
Getting a Spouse visa is complicated by the financial requirements.
I would assume the British citizen is also eligible for an Ancestry visa (or does his citizenship preclude that?). Thus the partner could come as a dependant and not be subject to the financial requirements.
Without checking, but due to the low outside of UK Ancestry fee, I suspect it is quite possible that it will be a similar or lesser total cost then applying for a spouse visa then renewing it.
So, if all of the above is valid, Ancestry dependant may be the better option.
Final question, when it comes to ILR, can the dependant only apply with the main applicant? Even if it is possible I can't see the point of the main applicant who is already British applying for ILR.