"I don't think that there is any tangible benefit to adding both names to the mortgage or the deeds. In which case why bother?"
There is the benefit of ensuring that the property will pass to the spouse\partner by survivorship (automatically) on death. If the intention is that the spouse\partner should instead get the house through a will, the following should be borne in mind:
1. Where property goes through probate\administration, the process could mean potential claims from others - such as your children, including (this happened with a client of mine) children the family did not know about.
2. Apart from the potential risk to the asset, the cost of probate\administration is not insignificant. If everything else is in joint names, then putting the house into joint names is perhaps justified on potential cost saving grounds alone. (actually, mathematically it probably isn't, but knowing the costs have been saved is probably worth something in peace of mind terms).
I started this post before seeing that juke had already covered the point more succinctly.