While understanding existing code during software development or reverse engineering, it is quite useful to be able to quickly see other instances of the same variable or function in the current code view. To enable this feature in Ghidra, I suggest you perform the following two configuration changes:
Under "Edit" → "Tool Options..."
1. select "Listing Fields" → "Cursor Text Highlight" in the tree view on the left and change "Mouse Button To Activate" to "LEFT"
2. select "Key Bindings" in the tree view on the left and assign a key you can easily press to "Highlight Defined Use" ("SPACE" for example)
Happy understanding!
Update (2019-11-22): Actually "Highlight Defined Use" refered to in item 2. of the above list is not the same as the highlighted parts from item 1 :sadkeanu:.