When it comes to re-investing back in to your adult business?

Do you take a percentage of your monthly income and put that aside for re-investments (traffic, content, better hosting, design, programming, etc) or do you tend to spend what you need to, when you need to?

I know a lot of off-line businesses take anywhere between 10-30% of their revenue and re-invest it into business development, i just wondered how the rest of you folks did it?

For us, we have a set budget each month, content, traffic, design, etc all has to come out of this budget (which im actually over right now, but dont tell Gary ) i just wondered how the rest of you went about growing your adult businesses?

Regards,

Lee