I disagree. Use one overdraft for the reasons your stating.
Then with the other one, take the maximum out you can, shove it in a high interest savings account until it need to be paid back, and then one it does, pay it back, and you'll have some money left thanks to the interest (if you put £1000 in for 3 years, you'd end up with nearly £200 free money).
If you know you can manage your money, I don't see why not do that. I'm personally not going to, but thats cos I know I'll probably forget about something lol. The only problem you may have is that I think both banks say you must be paying your student loan and salaries etc into the account to have an overdraft.