what u r saying is adjusting the shutter in Tv mode such that the body will give u the aperture u want? that's just wrong... similar theory applies to Av mode...
it's not a mere matter of convinience n getting used to.. it's a matter of practically and needs for the type of picture u want.
I think there is some misunderstanding about exposure and effect eg bokeh, trailing, etc
Exposure is about the brightness of the photo generally affected by shutter speed and aperture. In auto mode, shutter speed change in opposite direction with the aperture.
Hence if you increase the shutter speed ie from 1/10s (slow) to 1/1000s (fast), the aperture will decrease ie from f/13 to f/4 to get the same exposure (brightness). Generally, increasing one f/stop will decrease one shutter speed. Therefore, if good exposure is obtained with f/4.5 and 1/160s then the same exposure will be obtained with f5 1/125, f8 1/50, f11 1/25, and f/25 1/5.
However, the effect on the photo will be different. With small aperture f/large number, the depth of field in large (meaning the foreground and background equally sharp) but those with large aperture f/small number, there will be bokeh effect (subject clear, background blur), despite the same exposure (brightness)
Similarly, if you are taking a moving car, prolonged exposure time (slow shutter speed=1/small number) will give you a trail of light, whereas short exposure time (fast shutter speed=1/large number) will give you a stationary car. And all this will have the same brightness.
Therefore, when to use Av/Tv will depend on what effect you want, and not the exposure you want.
This is a brief explanation. If you find this not helpful or need to know more, read up the books recommended by catchlight or any basic photography book from the library.
P/S: there are other factors, but need to understand this fundamental principle before bringing in the rest.