I suggest to look at a similar question, but just the glass question here:
- Glass is a very smooth surface
- Glass shrinks when cooling to a degree it pops the print free on itself
- Glass is virtually impossible to scratch with metal scrapers
- Glass stays fairly flat under heating
- Refurbishing of the bed isn't needed but for applying your adhesion solution (Woodglue, Gluestick, Hairspray, 3DLac, ABS-Slurry... pretty much ANY glue can work
- Glass is one of the few surfaces upon which almost all materials can be printed without risking ruining your print surface on removal
- PETG is one of the few that demands some sort of extra adhesion material with glass, most others don't need anything.
- POM and some other materials love to rip PEI apart
- I had a huge PLA-print stick so well to a BuildTak that I had to cut the sheet off the bed to get it off
The problems are fairly evident on the other hand:
- Glass is brittle and shatters on impact or thermal stress.
- Good glass can become rather expensive if you want a super flat sheet in non-standard sizing and a specific type.
- Large glass sheets need a very even heater to prevent thermal stress.
Borosilicate glass ("labware" glass) is more resistant to thermal stress but also does not pop free from the print the same way as normal glass does. It is also more sturdy but MUCH more expensive. It also comes with its own problems:
Some people have experienced spalling in combination with PETG, as it created a perfect airtight seal, making an adhesive as a separation layer mandatory. This behavior was also reported for normal glass, which is why an adhesive material is strongly suggested for this material.