As a investment professional, how do you quickly understand portco companies?

I'm a MBB associate doing various projects for PE sponsors (from typical CDDs / VDDs to PortCo work such as e.g., challenging the BU's/managements business plan). 

Since I am a generalist, I am often times confronted with PortCos in industries that are complex and I have no prior knowledge in. 

Typically (on a PortCo nearing the exit) I receive the Sell-Side banks business-plan and am often overwhelmed in getting the gist of whats going on in the business. 

Different BU's, different sales growth, different margins, some grow in price some in volume, some slash OpEx and grow tremendously in EBITDA, others keep OpEx constant. 

Given that I never did banking and the typical consultant is not so deep into financial statements, I would love to hear how you approach that in PE. Like how do you cut out the noise? What is really important? How do I quickly get to an 80/20 answers to whats going on in the business to my internal leadership as well as the external stakeholders (often in the PortCos there are 2-3 guys that are on "our" side while we try go gauge whats going on in the BUs).