whinmoor85 Sure no one needs a refractomer (like most other coffee paraphernalia), if you’re happy you’re getting good strikes rate in flavour preference, without too much faff, then great.
But one of the other things I have learned is the simple, sour, balanced, bitter progression in extraction isn’t that simple, there are peaks & troughs along the way and if you work progressively from low to high, you can hit pockets of bitterness that might prevent you from pushing through to a better place.
Also note that taste forms the basis of correlating what the phases are and what specific faults taste like so you can recognise, tweak & avoid them. Whether dialling in with, or without a refractometer, taste is always the guide.