All Aeron stools, regardless of tilt option selected, have a knob that allows you to set the tension of leaning back to respond based on your body weight. Standard tilt has only this adjustment. The tilt limiter and seat angle option adds two other features. The limiter allows you to lock the back so it doesn't recline and also provides 3 settings between locked and all the way back so you can partially recline. If you lean back a lot or want to be more ergonomic and take pressure off your spine by distributing weight from the seat to the back (this is what leaning back does), the tilt limiter will come in handy to take pressure off your spine and encourage you to lean back more. The seat angle adjustment allows you to change the seat angle (the back moves forward with it) from horizontal to a 5 degree forward tilt. This feature is good for you taskers who like to lean forward when you work.