Your involvement is essential
People who work in web development companies are not mind readers. Their skills are in designing and building websites.
To do their jobs properly, they depend on input from you. This means they need you to be responsive and engage in the process. You have to make yourself available, for example, to attend project meetings and review design concepts.
When deadlines slip, because you or your chosen web company don't keep the project moving along, the likely outcome is a delay in your site's completion and launch. You need to consider what impact that would have on your business plan.
In particular, the bane of every web company's existence is the client that never has time to finalise their website's content. Don't let that be you.
Also, remember that your web company's people are almost certainly juggling numerous commitments with other clients. If you are dithering and other work comes in for them, your website is going to slip right down their list of priorities.
