Hello Toyotaman.
Firstly the legal expenses insurance offered under the motor policy will provide cover for motoring incidents, the household legal is different in that it will provide cover for a wide range of everday situations, such as disputes with contractors engaged by you at your home.
The motoring legal cover can be a good purchase, if you were involved in a non-fault accident would you be comfortable in pursing a claim against the negligent third party and their insurers for your policy excess, hire car, loss of earnings, personal injury? etc.
You will find that most insurers and some brokers will wash their hands of such recovery claims if you have not purchased this cover although help can be sought from such 'credit hire' firms such as Car Crash Line on an after the event basis. Not sure of the financial implications of this though and it would mean another company to have to deal with at a stressful time.
Whilst in my opinion this cover is valuable and takes some of the stress away in the event of a crash, it is overpriced by most insurers and remains a very important revenue stream for them.