Are you planning to grow from seed, shoot cuttings, leaf cuttings, seedlings? Sand is usually introduced into potting compost to aid drainage, allowing air into the mix whilst retaining moisture. Humus (well rotted plant matter) is in the mix for nutrients.
Seeds and cuttings will grow well in salt free sand (wash well before use) for about 1 month before requiring replanting or adding plant food. If growing in sand, use course grained sand not fine builders sand.
Growing plants in a soilless medium is called hydroponics. The growing medium is essentially there to support the roots and to stop the plant falling over. The medium should retain miosture whilst not remaining waterlogged.
Feeding will be required more frequently, however I recommend diluting the feed to 1/4 to 1/2 strength.
I hope this is of some help. If it's not at least it gave you something to read.
;-))

Hi Stjohntongue, you were really helpful! :o)
I just wondered about what to plant cuttings in Actually, I should have been more specific. Thanks again.
(This is a Guest question because I just couldn't be bothered logging in lol)

Hi, Pip, You can start you woody cuttings (trees or shrubs) in sharp sand, clay granule type cat litter, or even oil-spill absorbent. The cat litter might be perfumed but it won't harm your plants and the smell soon goes after a few waterings (and it's cheap). Don't use wood pulp/paper, or litter that clumps when wet. Oil absorbent is inert (contains no chemicals/fertilisers/nutrients) so it won't harm the cuttings but you will need to feed them after roots have become established (this depends on the plant species).
Sorry Pip. I can't really help you with non trees/shrubs as I grow mainly bonsai trees, but I'm sure some of our other members will be only too pleased to help.

Thanks for all your advice ;oD