Jobs round the home often need people from different trades. For example if your having a new bathroom fitted - you may need a plasterer, plumber and tiler. Local tradespeople often regularly work with people from other trades, so will be able to recommend to you reliable and honest people with good reputations to do the jobs you need. They will work closely together to make sure that the right people are on hand at the right stages of the job.
Larger companies from outside will often bring in their own people to do the work. The job may be done very well but if you run into problems, it is more difficult to have them put right if the people you are using are not on your doorstep.
The Best of Taunton promotes some great local tradespeople, all with great testimonials from there customers.