I love the colour that annuals give to a garden. I have pots on the front and back terraces and certain annuals I use in the herbaceous borders as well. I have a big garden, over an acre, which I have built up to have a basic structure of perennials, but there are always a few gaps and annuals, such as rudbeckias, salvia farinacea, cosmos, nicotianas fill in the gaps and provide colour right up to the frosts.
Last year a couple of moles decided to set up home in a couple of my large borders and with the plants there I hadn't realised the amount of damage. This spring I've been digging out all the tunnels which had gone under perennials and killed some of them, so annuals are filling in the gaps. I'm afraid the moles were dealt with last autumn.
It takes time for perennials to get to a decent size as French GCs sell them so small so annuals are useful while building up stock. I also have a few shady areas and I like Busy-Lizzies and bedding begonias to brighten them up. Ferns, I hear you say, but they don't grow well here and I do have hostas, pulmonarias, epimediums etc but I like the colour too.
So, a bit of everything for me, but then I'm lucky to have the space.