How Good or Bad is Faster Attack Support?

I noticed no builds, in my last year or so of playing PoE use FAS gem. Is it really that bad or only situational, like for leveling through campaign?

Not sure if this is a question only your char in PoB could really answer or if it's always best to go for a 'more' multiplier gem in your 6l set up regardless of atk speed.

It's easily one of the worst support gems available in terms of dps output. Worth using for movement skills if you have that free slot but nowhere else. There are just so many better ways to get increased attack speed that it's not worth wasting a gem slot for it that could provide you with a 4x% more multiplier instead.

Thanks.
That's more or less what I thought but wasn't sure how to go about calculating it on my own.

All I know is from 4.0 atk/s it brought me to around 5.0-5.10 but if my fail math is correct that's only around a 20% multiplier to dmg.

If you increase it from 4 aps to 5 aps that would be a 25% increase i.e 25% more damage. In itself that isn't even that bad, what makes the gem bad is opportunity cost. You can have increased attack speed on amulets, rings, gloves and weapons, as well as plenty of it on the tree. If you really feel like you need more aps you will get better results by scaling increased attack speed from those sources instead of via gem. Because none of those other ias sources can give you more multipliers.

you sometimes support movement skills.

If you had literally no other source of increased attack speed, it would be a 44% MORE multiplier (not counting quality). It would be 54% with 20% quality.

Most supports are like 49 to 54%.

As others have stated, the problem is there are already so many sources of attack speed, that if you barely try, you have a good amount. So its more like 20% to many builds.

I suppose for some odd tree in the upper half, with little or no attack speed, it would be ok.

it also has a defensive aspect. The faster you attack, the lower chance of enemies hitting you before you hit them. Shorter attack time also makes kiting with ranged builds more effective. While this can be irrelevant with already very fast builds, with slow weapons it can make a big difference, especially for attackers from the left side of the tree.

It would be hard to build a low enough attack speed to make it worth it. Assuming you are a chieftain, the slowest attacker of the marauder (both other ascendancies can increase attack speed), your first 50 points in 2h axe or similar would you get you 80% increase attack speed. Thats with hp and fortify nodes you'd want anyway....

https://poeplanner.com/AQACAA8AAQMANADcATwFdQeWCTwOIBRxFFUhdzAJMug2DjlSOvw9fkd4SEdQY1ivWP5ZP19SYVJkTWVGbGxy43cNeGh52YRghmqHz4x5l26plKnytTa9p74awKbABMGjwVPF2MYy3D3cYeJR5A7vSPbr-AAAAAADAAD______________________wAAAQAAAAMA_____________zwAAAAA

Removing all speed specific nodes, I'm still at 51%, which cuts the value of Increased speed in half.

https://poeplanner.com/AQACAA8AAQMANADcATwFlgk8DkwTIBRxFOEXVSH4JiAn-ywJMug2DjlSOvw9fkd4SDJOR1BjWK9YP19SYVJkTWVGbGxy43cNeGh52YRghmqHIorPjHmXbqmUqfK1Nr2nvhrABMFTxdjGMtxR5A7vSPbr-AAAAAADAAD______________________wAAAQAAAAMA_____________zwAAAAA

I can't imagine it being worth it.

My usages of it include attack movement skills (leap slam) and spellslinger (to precisely calibrate my attack speed).