Delegation is the key to growth. You can not develop new clients if your time is consumed with the needs of your current ones.
This concept is challenging for partners who pride themselves on the quality of their work product. After all, their clients have come to expect a certain caliber of service. Surely they will become disenchanted if their needs are pushed to other members of the firm.
But the fact of the matter is that your clients only care that their needs are addressed competently. And the key to growing your book of business beyond the choke-point of your own personal capacity is to delegate as much as possible so that your desk is reserved solely for the projects no one else can accomplish. That means spending time you often feel you don't have on regular check-in meetings with your team to ensure that they understand your directives. It means mentoring and reviewing others' work. But it also means coming to terms with the fact that the work you delegate will rarely turn out the way it would have had you executed it. You have to become less precious about the nuances that your clients barely notice anyway.
Most of the successful rainmakers I know are obsessed with leverage. They are constantly looking for ways to minimize the time spent on client service so they can focus more on client acquisition. Why? Because it's far easier to find a service partner than a rainmaker.
So, if you are frustrated that you never seem to have the time for business development, consider that you may have a delegation problem. You can solve this by surrounding yourself with a competent team and empowering them to take care of your clients. Let them focus on the short-term needs at the office so you can focus on the long-term growth of the firm.