One piece of advice I heard recently was 'spend the company's money and your time as though it is your money and your time'.
I've seen this work spectacularly badly at Universities, where every effort is made to horde the income from projects for 'rainy days', to the detriment of the project. Very similar to the way the project leader ran his own finances (lived like a pauper on a strong salary). This was really bad in two ways: His group constantly ran cost over-runs because of equipment failures because of the refusal to service or upgrade equipment, or doing specialist tasks in-house rather than contracting the specialist (usually the statistician). This also often breached the contract with the agency who gave him the grant money for his project! All the funds were for a specific project, not something else and not for profit (which is how 'savings' have to be catagorised here). What was worst was that he never spent those savings, the internal account he stashed his savings in kept getting (legitimately) skimmed to cover costs in other projects (company accounts aren't bank accounts after all).
Money, especially a clients money for a project, is to be spent not saved.1
1 This of course excludes the money marked as 'profit' that should be taken out of the project managers hands immediately, I'm talking about the money that was marked down as 'costs'. Never ever bloody ever run under budget.