Another article for all you Keynesians out there: More Government Spending = Weaker Economic Performance. And the article notes this as well:

• The OECD admitted in one study that “a reduction in the size of the government could increase long-term GDP by about 10%, with much larger effects in some countries.”
• The OECD admitted in another study that “a cut in the tax-to-GDP ratio by 10 percentage points of GDP (accompanied by a deficit-neutral cut in transfers) may increase annual growth by ½ to 1 percentage points.”
• The OECD admitted in a different study that “an increase of about one percentage point in the tax pressure (or, equivalently one half of a percentage point in government consumption, taken as a proxy for government size)…could be associated with a direct reduction of about 0.3 per cent in output per capita. If the investment effect is taken into account, the overall reduction would be about 0.6-0.7 per cent.”

Why this might be you will never understand if you start from Y=C+I+G, but that’s all you are going to find in any macro text anywhere in the world.