[maxloh]

> On the other hand, the more legacy you support, the larger your potential customer base is.

It is more a decision about the trade-off between costs and benefits. Supporting really old browsers like IE is a pain in the ass.

> Another is that you should regularly use the oldest platform (hardware, OS, browser) that you want to support.

It is possible to manually slowing down your browser with dev tools. https://imgur.com/a/99XbwN9