A use-case would be with a large stored procedure that either generates a report or performs some complex transaction. When doing some troubleshooting or bug fixing, there are often multiple columns or variables of special interest for the specific task. Today I had a case where I was trying to solve a bug in an SP that should trigger restocking when an order is inserted and the stock reaches under a specified level. The main part of the SP deals with inserting an order, so to find the code I'm looking for I search for "Stock" which is used in many places, then I select "@Quantity" and scroll through the document to find where these are used together. Unfortunately as soon as I move the cursor, the selected highlight disappears, and as soon as I hit escape the other disappears...
Another use-case would be with an SP that does some synchronization, for example xml is provided to the SP as an argument, and it should update a set of tables. Now an extra field needs to be added to the SP (and XML). An easy way to handle this is to pick a similar field already existing, and add the new field to all statements wherever the similar one already occurs in the SP. However the XML field may have a different name than the table columns, and different tables may have columns with different names that should be affected by the new field... In that case this task becomes allot more challenging, but a colorful multiple-search feature would greatly help.
I would also use the feature to discriminate between very similar fields, for example inc or ex VAT, purchase/sales price etc... These fields are used in multitudes of SP's and being able to color code them would relieve some strain on dyslectic eyes.
Here is a little mock-up of what I have in mind (the SP is not representative but it should give an idea):