The actual reason is to avoid taxes depends on the country where you live in, if the law is straight and pretty simple that you need to pay flat % of your winnings as tax no matter what then claiming as soon as makes sense but in many states government run lottery so they offer different options and one who withdrew all in once has to pay 50% as tax and one who take the rewards in the installments every month they will get 100% if their winnings with no tax deduction but it will take 10 or even more years to collect the rewards completely.