What use is a general purpose manager?

A while ago, I wrote an article about what makes a good manager. One of the assets that I thought a good manager should possess is domain knowledge. They should understand (even if only in broad terms) what the team does. A full understanding and appreciation of what your team does is important.

I would therefore fully expect a Finance manager to have a good understanding of finances, a Human Resources manager to have a good understanding of Human Resources and so on. It seems pretty obvious, but there seem to be managers who do not possess this domain knowledge.

Being able to monitor your team's finances, manage their appraisals and other such managerial duties is the bare minimum I would expect from my manager. All managers should possess these skills. Above and beyond having these basic managerial skills though, I would expect them to have a sound and broad knowledge of their particular domain.

As the manager of a Development Team, I have a broad and deep understanding of technology. I work hard to keep myself abreast of new and emerging technologies. I fully understand what my team does, what we are delivering, how it can be delivered and what is possible.

More importantly, I am capable of making decisions. This is one of the vital duties of a manager. By fully understanding what my team does, and taking an active part in the day-to-day work of my team, gives me a deep understanding of what we do, which allows me to make decisions on behalf of my team.

I am very much a hands-on manager, and get involved in much of the day-to-day work, because this is the work that I enjoy the most. As a manager, I also have to undertake all the other managerial duties as well though.

I genuinely fail to see how you can make decisions without understanding what your team does. I could of course ask the team, and I would expect any manager to do this anyway. However, the final decision would need to be made by the manager, as this is ultimately their responsibility, and is what they are being paid for.

If they can't make those decisions, then why are they in charge?