From BlenderWiki

UI Violations regarding the usage of the LMB and RMB

Separating Selection from action

The following rules apply to the default usage of the mouse buttons:

• RMB: To select an item
• SHIFT +RMB: To add/remove more items from the selection
• LMB: to perform an action on the selection

Please remind: This is not about whether LMB or RMB should be used for Select. This is to find where the rules are violated and why it possibly was a good idea to violate them.

Deviations from the rules

Unfortunately there are a few corner cases where action and selection might intertwine. And some parts in Blender even violate the principle such that now RMB selects and LMB takes action.

Here is a list of deviations from the Blender concept within the various available editors:

 

In the View port

Object Mode

• RMB + Tweak: selects an Object and starts a Transform (move). This operation mixes Selection and Action.

Edit Mode

• RMB + Tweak: selects a vertex/edge/face and starts a Transform (move). This operation mixes Selection and Action.

Sculpt Mode

OK

Vertex Paint

OK

Weight Paint

OK

Texture Paint

OK

Timeline

• RMB + Tweak: selects a Marker and moves it. This operation mixes Selection and Action.

Graph Editor

• In the channel's panel, LMB is used for selection

Dope Sheet

• In the channel's panel, LMB is used for selection

NLA Editor

• In the left-hand tracks panel, LMB is used for selection

UV Image editor

Video Sequence Editor

Movie Clip Editor

Text editor

• RMB gives action menu. It does not select, breaking the Action | Select model.
• LMB + Tweak selects text.

Node Editor

• RMB + Tweak: selects and moves node. This operation mixes Selection and Action.
• LMB + Tweak: selects and moves node. This operation mixes Selection and Action.
• RMB + Tweak: selects and moves reroute This operation mixes Selection and Action.
• LMB + Tweak: selects reroute and extrudes noodle. This operation mixes Selection and Action.

Logic editor

Properties

Outliner

• LMB for selecting. Unsure if this is a violation. Is it? Buttons are all selected using the LMB ...
• RMB both pre-selects and pops up action menu for highlighted item. This does not actually select item, unless chosen from action menu.

User preferences

OK

Info

• RMB selects Text Elements. In all other areas of Blender text elements are selected with LMB
• RMB on a selected Element unselects it. In All other areas this is done with SHIFT +RMB

File Browser

• LMB can be used for Select
• LMB+tweak adds to selection (as if it were with shift). RMB+tweak does nothing. Shift+LMB+tweak does weird things.

Python Console

• LMB +Drag selects text parts. While this conforms to operating system standard behaviour, it actually violates Blender's rules(Select should be done with RMB).

UI Widgets

• Lists items (UILayout.template_list) are selected using LMB regardless of the setting
• Menu items are selected using LMB, (but often they initiate an action, so it seems OK)
• The Color Ramp widget has LMB for selection and LMB+tweak for moving. RMB invokes menu. Ctrl+LMB creates a new point, regardless of the setting
• In the Curves box (such as RGB Curves node), LMB selects a point. Shift+LMB selects multiple, which is mostly useless