msata with expansion board or external ssd

[curious]

I am planning to move from a sd-disk to a ssd.
Much is written about an expension board containing sata to usb and a msata ssd

Is this combination better than a normal ssd and an usb cable ?

I know it takes less space, but a normal ssd is easier to connect to a pc when flashing or copying.
Are there limitations to the size of an external ssd when connected to a raspberry, and can I use evry usb-cable ?