I'm not 100% on this, but I understand that SAAS will pay for 100% of the tuition fees for Scottish students in Scottish universities, whereas in England, the student has to pay their tuition fees. However in England every English student is entitled to a loan to cover the tuition fees (up to £3225 this year, the maximum UK tuition fee), as long as the university is within the UK. The money is transferred directly to the university, so if you go to as Scottish university where the fees are £1820 to English students, you cannot ask for a £3225 loan, and keep the excess.
Every student is also eligible for a maintenance loan, and the amount available is dependent on your household income. Those with an income below (£52k?) are also able to get a maintenance grant, which doesn't have to be paid back. However if you receive a maintenance grant, the limit of your maintenance loan may be decreased. The maintenance loan that you receive in the first year will remain the same throughout your time at university unless your financial circumstances change (for example the people I know in the same financial circumstances as me who went to uni last year will be able to get £1200 a year, every year, more on their maintenance loan than I will going this year)