[Karellen]

> Most companies don't prioritize legacy support,

On the other hand, the more legacy you support, the larger your potential customer base is. Also, if everyone else in the sector only supports the most recent release of only two browsers, you might have that extended customer base all to yourself.

> you would better develop your app using the latest dev tools and targeting the latest web specifications only.

That is one school of thought.

Another is that you should regularly use the oldest platform (hardware, OS, browser) that you want to support. That way you won't get to two weeks before release, decide you ought to test on a dual-core 4Gb machine like you were planning on supporting, and realise that although it technically runs, it's so frustratingly slow that no-one would want to, but there's not enough time to make the changes you'd need to get it working "acceptably". OTOH, if you were using it on hardware where it ran like a dog for you from the 3rd sprint, you'd probably have got round to making the changes for it to be acceptable on that era platform.

[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

[account42]

> OTOH, if you were using it on hardware where it ran like a dog for you from the 3rd sprint, you'd probably have got round to making the changes for it to be acceptable on that era platform.

Or perhaps even made saner choices in the first place rather than rambling about "premature optimization".