It's both many times faster than booting from microSD, and unless you buy the absolute cheapest SSD from a no-name manufacture, many times more reliable.
Additionally, if you have a good power supply and don't write tons of data on a daily basis to the microSD card, it will be quite reliable as long as it's a name-brand, high quality card.
Source: I've deployed about 50 RPis in various conditions, all but two booting off microSD cards, and have only had one failure requiring swapping in a new microSD card, over the past 8 years of use.
Industrial microSD cards are especially robust and are now available from a variety of manufacturers with environmental and wear ratings that rival decent SSDs.
It's not so much about the SSD, but the USB cable being quite easy to unplug accidentally, though I suppose if you used something like one of those short Samsung Fit drives or a NVMe dock and had a custom enclosure that holds it in place after the Pi is screwed in, then maybe yeah.
Why not? There are plenty of RPi enclosures that will bridge to USB and hold the SSD for you. For me, the cost of an RPi 8gb + enclosure + ssd + power is now close to the micro intel boxes.
Additionally, if you have a good power supply and don't write tons of data on a daily basis to the microSD card, it will be quite reliable as long as it's a name-brand, high quality card.
Source: I've deployed about 50 RPis in various conditions, all but two booting off microSD cards, and have only had one failure requiring swapping in a new microSD card, over the past 8 years of use.
Industrial microSD cards are especially robust and are now available from a variety of manufacturers with environmental and wear ratings that rival decent SSDs.