What does the “remove doubles” option do?
It takes all vertices based on your selection and merges them together based on proximity. The default is a proximity of 0.0, meaning the operation only merges vertices that are completely on top of each other.
The proximity threshold is set in the operator menu “F6” after choosing Remove Doubles. The operator menu can also be found in the bottom of the T-panel.
It is useful in a variety of situations like cleaning up loose double vertices which may cause shading issues if they’re connected, and also a quick way to mass weld vertices that are close but would otherwise require manual labor. It can also be a wildcard that messes up if you’re not mindful of both your selection and the proximity threshold.
Be careful when using remove double…E.g…If You have applyed a Edge - split to the Object - It will be removed when You use Remove doble…