I rarely use plans. Sometimes, if dimensions are important, I’ll sketch things out to make sure I get it right. Many of my projects come from the wife seeing a picture in a magazine and asking if I could make it for her.
For large projects, measured drawings, cut lists, parts tracking lists are in order. The wife wanted interior shutters for 6 sets of sliding doors and 4 windows. All 3 panel double bi-fold. Keeping all the parts straight was a real test of my poor organizational skills.
When I have used plans, they always get modified to suit our needs. Sometimes it is changing joinery, other times dimensions.
I keep a sketch pad handy at work to capture ideas. Helps to sketch things out a bit.
-- Sawdust Maker