Please have a look at these projects:
In this one Monty talks about spacing potatoes, and the different effects you can get from spacing them far apart or close together.
Here, Chris is talking about overwintering onions, and the spacing you'd need for those.
This is Monty again, talking about pea seed spacing. In this case he's spacing them as close together as possible.
There are other videos. If you put 'space plants' into the new search engine you will find them. As a general rule, spacing close together will give you smaller crops that can be just as good. However, fungal diseases can be harder to control because the plants have less air in between.
Please do keep looking at the site as we are keen to put up more information for people with mobility problems. If anyone has any areas they'd particularly like to know about, please do share them with us.