Last fall I put our shredded leaves on the garden, do I leave them?

Work them into the soil of your garden. They add nutrients into the soil as well as compost. Your garden will thank you.

You can rake them off, but you can also till them into the soil. If you rake them off, do you have a composting area? If so, add them to that for next fall

No I don't have a composting area. Thank you for comment

They should be cultivated into the soil to discourage slugs and other insects from breeding under them.

You can work them into the soil

It actually depends upon the type of leaves. If they are oak, rake them off and dispose of them. Anything else is OK to work into the soil, although I'd rather see them in a compost pile to decompose.

I do this every year. Earth worms breed like crazy under there and the little buggers enrich the soil with what they leave behind.

I pull the leaves back in the Spring and plant my plants. Same as any flower garden, the tomatoes and peppers, etc. benefit from mulch. Shredded leaves are the best mulch there is, just don't smother your plants. They need a little breathing room.

By the time the new crop of leaves is ready in Fall of 2018 the worms will have consumed last year's leaves. Less work weeding, enriches the soil, and gives a place to dispose of the leaves from the driveway or that would be smothering your lawn. Is there a down side to this, besides the work to gather, shred, and spread? Don't think so.