When you look at renting an allotment or having your own allotment for growing stuff in your own home, I think that most people would reasonably feel that having the space to do it in your own home is better. This may be the case, put privacy and easy access may not be enough to offset the benefits to having your allotment in and amongst a number of other people’s allotments.
Being around other people doing the same thing is almost always better, because it means that you can share your knowledge and skills. In the case of growing food in an allotment, you’re often limited in the number of things you can grow too, so it can be a great option to barter what you’ve grown with what other people have grown in their allotment, in addition to having all those people around you to exchange your knowledge with.