When the need to connect multiple lines arise, there are different methods you can use, but probably the commands most used for that are Fillet and Chamfer.

Regardless of the command chosen, when you need to use different radius values, it’s a bit annoying having to change the radius value for a particular pair of lines, and then reset the value before move on to the next one.

Saying this, if the radius value you need/want  to apply is 0, you don’t need to change the Fillet Radius value. Try this:

-          Launch the Fillet command

-          Select the first line

-          Press and Hold the Shift Key

-          Now Click the second Entity

As you can see, using the Shift Key overrides the default value of the command. This process is also valid for the Chamfer command. You can apply an acute corner by pressing Shift and specifying the second drawing entity. This method creates acute corners without changing the chamfer distances to join two end points.

See the image below showing the results of using the Shift Key in both commands, and for comparison, the results without using the Shift Key.

Fillet/Chamfer + Shift Key Demo