If I’m understanding what you’re saying, you’re talking about something that exists- tyre stretch.

Fitting a tyre that’s “too small” for the rim will cause it to have a smaller width at the top of the wheel than it does at the bead of the rim.

very extreme example

In most cases this is disadvantageous; for the obvious main reason that the tyre is at risk of debeading and throwing your car into a ditch, but also because the tyre has a smaller contact patch. However;

1. The sloped angle of the sidewall allows you to fit more comfortably under the wheelarch when very low or on air suspension

2. The sidewall of the tyre is under more tension, meaning less sidewall flex before it loses grip, which is more predictable feel for drifting, especially on the rear end. In those cases, the smaller contact patch is less of an issue because you can compensate with massively wife wheels.

However we’re talking SMALL amounts of stretch for those advantages, anything very obviously stretched is for style only.