Take a long time to complete the application
Take a lot time for the granter to make a decision
You may not get what you want
My view is that if you view the funding as an investment that you wouldn’t make unless you got a grant (could be because it is at the cutting edge of technology / high risk of failure), then grants are a good source of funding. If you believe in it and there are other ways to fund it, i.e. debt / equity, then you have to weight up the pros and cons of free money vs time.
So, I signpost people to grant funders – I don’t complete the paperwork. I will refer on to grant writing specialists as often it isnt what you are doing that is the issue – it’s the way you tell them!