grafting is only really worthy if you're trying to grow a variety that does poorly in your area or suffers from certain types of diseases. typically, grafting is done for better resistance to soil diseases and pathogens such as nematodes. grafting can increase fruit production and size, but it depends on the variety and the type of rootstock used. the increase is caused by using rootstocks from vigorous growing species with specific traits which can enhanced water and nutrient uptake in macronutrients (ie phosphorus and nitrogen).

however, for most people, grafting is a waste of money. if you live in an area that is problematic for certain types of fruit, then you can benefit by growing grafted plants. for example, lets say you live in a cool area - getting tomatoes grafted onto a rootstock that is less prone to thermal stress in cool soil could be a benefit.

another reason why you might consider grafting is if you want to grow a specific species that is notorious for lack of production. grafting such plant to a more vigorous growing rootstock can help. however, with the thousands of tomato varieties, you're likely better just planting another variety with better growing characteristics. for example, if you like Roma tomatoes, but want a more productive plant, you could just grow Amish Paste, San Marzano, etc.. which are more productive and less susceptible to BER, not to mention, taste better :-)

I tried grafting beefsteaks to one of the rootstocks, I forget which, the one most appropriate. I had problems because the rootstock seedlings grew much faster than my scion plants. So had trouble matching sizes. You have to plant some rootstocks much later than I tried. I tried 1 to 3 days later for the rootstocks. So I put them in a deep covered bowl and they all blackened, mold, fungus or what ever.

I tried apple tree grafting last year. A Redfield, a McIntosh, and a Black Oxford. They all took including s spare for future use.

The varieties, used as root stock, in addition to being resistant to some soil borne disease, also grow big vigorius roots. Well, obviously, bigger, healthier roots provide more nutrients to the top. So this might in some cases translate into more productivity. I have heard some gardeners swear by it. Some say it make no or very little difference in terms of production. I, personally, won,t go that rout just to get a few more tomatoes. Instead i would just plant an extra.

YMMV.