I do this fairly regularly for my clients (am a will writer). It depends on your reasons for doing it; usually it's in a blended family situation, and is intended to prevent the surviving spouse leaving the joint estate either just to their joint children, or a third party, thereby depriving the children of the first relationship. In those circs, both parties are usually on board with the idea and there's no conflict.
Or the reason may be that the client inherited most of her wealth from her parents and knows that they would lhave wanted to pass the money down through the generations.
Sometimes, people give life interests or rights to reside because they happen to be married to someone who is very bad with money, or is from another country and likely to return there (if that country's inheritance laws are different from the UK that can be a big problem).
I generally suggest to anyone I'm acting for singly, not as a couple, that they blame me. I'm happy to be the bad cop, "insisting" on a life interest if the client feels uncomfortable taking responsibility for the decision. It's easy for the client to tell her husband (it is usually the husband), that although she wanted to give him everything, the will writer insists that a life interest is the only sensible option in the circumstances. The husband can then rant and rave at or about me, I don't care, and the client gets what she wants.
OP, if you're interested I have a paid for ad over on the Small Business Section of Classifieds.
I'm running a special offer at the moment for families with special needs for anyone that may apply to.