Auto Levelling - Why?

I have built 3 Prusa i3's none of which have auto levelling.
I have a solid spacer on the home position corner, 3mm bolts with springs and nylocks on the other 3 corners and a micro adjustable z endstop.

I set the home position corner then go around the other corners, then re-check.
Once this is setup I don't have to check the corners unless I move the printer itself - I just check the z home position height and adjust it if necessary.
I only usually check this when I change filament and most times I don't have to do anything.

So why bother going to the hassle of adding a probe system?

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My updated Instructable on our Prusa i3 Build
[www.instructables.com]

I agree , I was considering using a dial indicator but if it was mounted at the side where the auto level sensors are then it is not measuring at the exact point of the nozzle location anyhow so I do the manual thing. I started using the LCD positioning for the xy positions which was a pain. So now I get both Z axis lead screws same height then I Home all axis then disable the steppers after having set Z axis min and move the table by hand to the four corners and adjust level screws. I do this before every major print as I found that pulling parts up and cleaning the bed affects the level.

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rwt

I agree too. My Createc Psique i3 Steel never needs adjusting. And there is less weight on the extruder with no ABL.

It's all about a solid frame.

I fail to understand this "autolevelling" for Cartesian machines. All axis must be set square and the flat bed too. You do it once. If you have to redo it often, the design, the assembly, the parts ... are simply poor quality and must be fixed.

Auto level is nice to account for the bed surface not being perfect. And for the small amounts it changes if a print it particularly difficult to remove, or when you clean the print surface.

I don't care how how rigid you make the frame and trolley and bed, when you are talking about hundredths of a millimeter making a difference, every little bit helps.
There is a reason multimillion dollar cnc machines check their planes as a calibration.

I had an old Makerbot and never really thought about auto-levelling even when my platform was not completely flat: [www.thingiverse.com]
But I am now trying to make a chinese prusa i3 work and I am pleased with the automatic levelling. I am not sure if the bed it is slighty bend because the pressure the springs put on it, but when checking with a metallic ruler there are small imperfections and the auto-levelling deals with this greatly.

Maybe is not a must, but certainly is an easy way to go towards better resolutions and printers.