Answer:
Wow, line printers... Many now in museums.
Advantages? They're very fast and also impact printers. If your needs require multi-part forms, then you must use an impact printer, either dasiy wheel or dot matrix.
Typical main-frame line printers (IBM) use a metal "band saw" character loop, and solenoids for each character position, typically 132 columns. The band spins at several RPS and as each letter aligns with the column it's intended to be, the solenoid, or hammer behind that column fires striking the letter through the ink ribbon, onto the paper.
The speed is obvious. Since each letter passes each column several times per second, the entire line of print can be struck at once. 10 lines per second is typical and the sound is quite high; necessitating heavy sound insulation.
Disadvantages:
The standard "line printer" can only use pin feed paper, cannot use other than standard widths {17"} typical, and is pretty specialized to the system being used. No color other than black.
Summarizing:
They're very fast, faster than most other technology, can print multi-part forms, something only impact printers can do, are large, loud, and something not available in the general retail system. An office desk takes up the same or less space.
Watching one print 10 lines per second, entire lines at once is impressive.
Oh a final disadvantage: price. They're not your $99 home photo printer! About 4 digits last I checked (mid 80's, IBM system 34/36, slower and less RAM, HDD space then a standard desktop! - but multi-user, mutitasking - with green on black monitors)