The bulb needs to be replaced because it looses the proper wavelength over time. The bulb still lights up, but looses effectiveness at sterilizing,
The unit going on and off may slightly (very) effect the lifespan of the bulb in terms of the bulb might blow (meaning it won’t light up). Ever notice your house light bulbs more often blow out when you turn em on... quick change on temperature, materials expanding, blah blah blah.
Can’t see the transformer being effected by going on and off.
You buy and use a uv for a purpose. Depending on size, flow, what you want sterilization to accomplish, run it as you intend. Not because the bulb lasts longer or out of fear that there a small change your bulb might blow.
I usually order a few bulbs at a time anyway. If bulb blows, change it.
Cleaning the sleeve probably shortens the bulb life in terms of it blowing out more than anything. Don’t find them to get too dirty. Or for that build up to effect the effectiveness much. I only clean when o change the bulb.