Management accounting is about creating custom reports for the business owner that are more meaningful and beneficial. 

As a business mentor this is exactly what's covered in my Academy of Business Mastery training course. While the training is to a small group of 3 business owners only, each business' Chart of Accounts is reviewed to customise it for more meaning. How to read and understand a Profit and Loss is also covered.

There's far more to running a business than just finances as this is just one aspect of any business.

The other two aspects custom reports are needed for are sales, marketing and service work.

Tracking how many sales are coming in each week as a dollar figure, that is then compared to the dollar value worth of work 'produced' in the week, and then accumulated over a month determines whether work loads are increasing, requiring an extra employee or decreasing meaning the business is over staffed.

When a business is understaffed, the business owner has to get more 'hands-on' and stops managing their business.

When a business is overstaffed, cash reserves start to be consumed. So understanding the sales to work produced ratio every week is all part of management. These aspects need to be measured because they greatly effect what will be seen in the financials.

Financial reports don't tell a business owner so many things so just having custom reports for finances is only a small portion of what's required with management.

Knowing how many leads your business needs each week on average, to produce what is the average number of sales and income is very important.  A financial report won't reveal these things.

Tracking the gross margin (with employee labour included) is super important on each and every job, to see if it was under or over the required gross margin figure (seen on a yearly P & L) is important.

The P & L only shows the average gross margin and only accurately for time frames of 3 months or more in a lot of businesses, so tracking grosss margins on individual jobs is far more important. A P & L gross margin for a month is often inaccurate due to the income not being related to the wages paid for the same month. Income is often received (if on Cash not Accrual) for work carried out weeks or months prior so it doesn't match the wages in the month. Materials often are purchased for upcoming work, or paid in a month on 30 day accounts, so they often don't match wages and income as well. 

While managing accounting has its place there's more to managing a business successfully than just accounting.  Different industries benefit more or less with it too so talking to an expert on measuring, KPIs and margins and how to increase them may be best.