Only have 5 years on the clock as a controller, but I've seen sitiations that made me uncomfortable. A/C coming in very hot and high on visuals due several things, and on ILS/LLZ due over correction due temp and/or wind on a tailwind (on req) approach.
I've spoken up a couple of times, in the polite "..you are 10nm from THR, are you able to make it straight in..." while at 5500ft on the ILS kind of way.
Some elected to go arround, some pressed on, and used all 2.5km to get it stopped.
A collauge in Sweden (many moons ago) had a Spanair MD80 do a 360 on final in sh**e weather to loose hight. It lost ground reference and performed a missed approach way offset from CL and bottomed out below the treeline in the vicinity.
He beat himself up for not refusing the orbit.
It's difficult to know when to speak I think. I got a bol***ing from a pilot because I pointed out that mode C indicated that he was not correcting for temprature and/or had the wrong pressure setting. (-28C at the time)
I was told to mind my own etc.....