It's hard to answer this question for a single player game. I guess it'd be the things that trivialize encounters and/or get over-used to the point of being boring and predictable.
I cheese the vendors, thieving like crazy with Feign death, but there is a natural limit on this. It gets repetitive. And with so many magic items in my camp means I spend time sorting. Boring.
On the other hand, when I've got resources to beat most encounters, it feels like I've worked for that.
And there can be a level of immersion there too. My Tav doubts he can pull through, so reluctantly agrees to Gale and Astarion's antics.
The worst offender I can see are using broken options. Tavern brawler looks super OP, as does those full Dex medium armours. I've mixed thoughts on wet condition with cold/lightning. The action spent on set-up kind of mitigates the cheese.
