Labour had to fill the holes left by the Tories. The NHS was on its knees - people were dying on waiting lists for operations lasting up to 18 months and more. One small example - there's a surgical procedure for certain heart patients that is most effective within six months of a heart attack. After that point, it may well be useless. The waiting list for surgery under the last Tory govt. was a year. The surgeon who told me about this was in despair - he said it would actually be more effective just to operate on people whose names began A-M and ignore N-Z as at least then some people would benefit.
Same applies to education - Tory cuts had left children in damp, dilapidated, leaking miserable schools. Labour had to put right the damage.
However, to assuage the city and look like 'New' rather than 'Old' Labour. Brown dreamed up hideously expensive ways of filling in the gaps, such as PFI. It was a way of stuffing money into the pockets of private sector firms. The Tories were all in favour, but it is doing us tremendous damage - all in the name of placating the City, the Tories and the economists who preach 'public sector bad, private sector good'.
Yes, it would make sense to run a surplus in good times, and you could do that far more effectively by building schools and hospitals out of government borrowing, rather than raising money far more expensively via PFI.