I didn't realize there was an undo feature now! Havent' done any sequencing for probably for about a month or so...
After you add or move an effect , right click on the grid , and then you can select the undo.
After that , you can undo the previous action etc. Not sure how far back u can go ...
Note that , you need to render or save for the undo to reflect , unless you drop another effect over the previous one.
So , if I dropped effect A on the grid , played, did not like it, undo, drop B where A was and played , no prob.
But if say I dropped A, did not like it, so undo, and then play, you will still 'see' A playing.
Click on the render button , if u wish to force it right away.