It's just the big odds that make it appealing shaun. I place multi's myself quite a bit on saturdays if I find a couple of ones i like in the $2 to $5 range, but thats just my recreational punting. Doubt you'd find many professionals using multi's.

They are pretty handy for sports as well, often place multi's on a few AFL games across a round or NBA games in a day when there are a big card of games. But at the end of the day its just the big odds for small outlay on events you think will win that make it appealing. It's not like there are any bonuses available or anything that make it more or less viable.