We collect it all year and then in Spring we shovel it into the hothouse and it makes fabulous fertilised soil for our tomatoes. Sometimes we even get a surprise vegetable out if it, last year we got rogue pumpkins in the hothouse.
We dig it out all year round (as otherwise we run out of room in the compost bin!) and use it to replenish the soil in our flower beds. We have also built up one bed in the past, to make it raised above ground level.
It also has a secondary use, to put off other cats from coming into our garden. We use compostable litter in our cat's litter tray, so when the compost is spread out in the garden, it carries his scent and marks the garden very firmly as his territory.