I just put mine on the compost heap, when I had one. Never found them of any use at deterring snails or slugs, or if they were, the effect was so minor it was unnoticeable.

I think the baking is just to clean off any egg white. Slugs will actually crawl over most things except maybe copper bands.

Thanks Bamboo and Volunteer
Some people say they work don't they, but I've never found them to be much good. Think I'll go back to putting them in the compost bin, although I have to crush them for there too as they don't break down.

Mbdog, I'd avoid composting egg shells altogether as they attract rats.

I rinse and then save mine all winter.I just crush them and put around young plants. I think the secret is not letting the circle become broken so I check them most days and fill in any breaks. They work for me.

I've never noticed them attracting rats. they would have no real nutritional value. They take an age to break down so crushing them helps.

They keep my snails out too...>)

Thankyou so much to everyone for your answers. It seems weird that they work for some people and not at all for others. The only thing I find works for me is copper rings an this year I'm gonna get some copper tape for the pots.
I'm wondering now whether crushed eggshells could be used in clay soil as an improver in the same way that we use grit.
Sorry for delay inthanking you all - I've been away and offline.