I mean it makes the game less fun for me. I enjoy running monsters and tactical combat. I like using cool and powerful monsters (as appropriate for party level). I like using some semblance of strategy and making my monsters behave in a way that is realistic for their stat block. It makes running the game less enjoyable to be faced with the choice of 1. nerf the monsters significantly to remove all real danger to the party and be easily defeated 2. choose suboptimal behaviors to minimize damage to PCs or 3. Risk a TPK on an encounter that shouldn't normally produce a TPK