Read enough writing advice books, and sooner or later, your head's going to ache.
'there are rules - but nobody knows what they are' - is a common meme among writers.
I've been lucky to belong to a very tough critique group since 2004. We know 'the rules', and sometimes, the rules must be ignored. The bottom line is - does your story keep moving, does it keep the reader engaged? Or do they yawn and put it down - perhaps to never pick it up again?
One of the things we've discovered for sure is - when the writing is chock full of 'had's, 'had been's, 'that's, and 'ly' adverbs - it 'slows' everything down. Oh, it doesn't matter so much in a paragraph or two, but if such boring, extraneous words populate your entire book, it can lead to lethargy. It just 'feels' slow. The reader doesn't know exactly why they don't pick up the book again, but they know it makes them not interested enough to continue.
Everything you do as a writer should be aimed at one goal - make the reader keep turning pages. Make them not want to put it down. Getting rid of unnecessary 'that's and 'had's helps with that - it makes the reading feel more active.
So, when are they unnecessary? here's an example of when you can get rid of the 'had's (and a 'that'):
Four years earlier, she had designed the woman's penthouse. She had purchased that ten-thousand dollar sofa that had been such a boondoggle. The woman had been thrilled when it arrived.
So - a more active way to write it:
Four years earlier, she designed the woman's penthouse. (since we've told the reader it was four years ago, the had is not necessary.) She purchased the ten-thousand-dollar sofa that became such a boondoggle. (Don't need the 'had' or the 1st 'that'.) The woman loved it when it arrived. (Got rid of the 'had' & by using 'loved it' instead, we also get rid of the passive 'was thrilled' that would have replaced the 'had been thrilled'.)
Read over your sentences, and if they make sense without the 'had', 'had been', or 'that' - leave them out. It just reads faster.
I believe the only way to get through the slings and arrows life throws at all of us is to find the humor.