With respect to the original question...
I use the retainer washer/clip (it is not always a washer) with any T-Tracked miter track that allows their use. As others have mentioned, not every miter track is 'T'd (as in T-Track), some only allow for the 3/4"x3/8" bar.
The purpose of the washer/clip is to positively retain the miter gauge in the slot when it is pulled forward beyond the front edge of the table -- such as for wide boards -- whether it be at the tablesaw, bandsaw, router table, etc. With the washer/clip installed the miter gauge will not tip up precariously, nor will it crash to the floor when extended beyond the front edge of the table.
I have never found mine to be a hassle so I always leave them in place for any tool that has a true T-track, but I will remove them when working with a tool that does not. To easily remove a miter gauge with such a retainer, you can either simply pull it back fully until it is free OR you may push it forward until the retainer washer/clip clears the rear of the table and then lift the miter gauge up and clear of the table.
As with much in woodworking, it is very much a matter of personal opinion and is not mandatory. If it really hassles you, go ahead and remove it -- just be careful when mitering or cross-cutting wide boards where the miter gauge must partially extend beyond the table's front edge.