There are a number of reasons why saving your own vegetable seeds is a good idea.  They are :

Once you have saved some of your own seeds you will realise what a rip off bought commercial seeds are.  It costs dollars to buy a seed packet with a few measly seeds in it when one vegetable plant left to go to seed will produce enough seeds to fill dozens of packets of seeds!

Saving your own seeds is easy, especially if you stick to the self pollinated vegetable varieties (See the Seed Pollination Section for details).  There is no special equipment required, just a few simple household and garden implements.  And it does not really take that much time.

But Perhaps the main reason why I grow a lot of my own seeds is quality.  A number of people I know have a preference for buying organic certified seeds.  I have bought both organic certified seeds and standard commercial ones and frankly I can see no difference between them.  But where I see a massive difference is between bought seeds and my own saved seeds.  My seeds have uniformly higher strike rates and  produce vigorous seedlings, so vigorous that at times they seem to come up like a cavalry charge!

I believe this is because my own seeds are harvested from plants that have been grown in my garden's soil and temperature conditions.  Commercial seeds are usually grown hundreds of miles away from my garden and sometimes even in different countries.

Commercial seed companies tend to concentrate on commercially viable vegetable varieties  which don't always have the best flavour or vigour.  While some smaller seed companies, such as Diggers and Phoenix, stock rarer heirloom varieties many seeds grown by vegetable gardeners cannot be found in any shop or seed catalogue.  By saving your own seeds you can hang onto some very unique vegetable varieties.  And as you will always have plenty of surplus seeds they become a great currency for swapping your seeds with other gardeners' seeds.  May of my best vegetable varieties came from home grown seeds given to me by other gardeners.