Enlighten me about plants needing a "mate"

[MrsFogi]

I'm a rookie at this gardening lark. Now, I know that tomatoes and other fruit trees often need to have a second in the garden to ensure pollination. But do other plants need such companions too? I ask as I'm about to buy lots of flowering shrubs and wonder if I need to double up on what I choose?

This is a good site for veggie companion planting. The fact that it's au makes no difference.

www.sgaonline.org.au/companion-planting/