Printing with no glue

i've printed thick walls but nothing more than 50% of the bed 
is it bad for the printer?

I use sugar water (1 part sugar dissolved in 2-3 parts water). Ratio isn't that precise. Works great for PLA, ABS, and PETG. Put a small amount (nickel-quarter size puddle) in center of clean bed, spread with a paper towel, heat up bed and go. Parts come off easily after cooling back down. Don't try to remove warm or you will remove the sugar coating/crack your glass. Usually replace every 10-15 prints or if I notice it not sticking as well.

If you live in Texas or any of the southern states DON'T try sugar water unless you want fire ants becoming full time residents in your home or print space. Enough to cover a bed on a printer will give off enough odor to bring them from miles around. I would stick with hairspray myself. It works great and you will actually hear the part pop loose once the temp gets below 40 or so and it will lift off with no effort.

I no longer use a Da Vinci but most just make a cardboard shield while spraying.. Or you get a different glass plate which is what the rest of us do to protect the stock one as it is very hard to source. Then you just take it out, spray it and put it back in. Once sprayed it is good for a week or more of printing. Just go to a glass shop and get them to cut 3mm thick tempered glass to the stock bed dimensions. All you have to do is adjust your z offset to compensate for the additional 3 mm. The mounting tabs on the stock glass can be used as the screws are long enough.

Another option is to use kapton tape and glue.
That means you just need to peel the tape off when you need to renew it and saves having to clean the bed.

Talking about glue.
I've been printing on the tape that came with the Davinci Pro, painters tape, kapton and now on glass.

The glass is nice, cause I can take it off the bed with ease, and clean it easily in the sink.
I still use some glue (from Pritt).

Question. When do you guys put the glue on? When the bed is hot or when it's still cold?

I use elmer's gluestick and if you need to clean the bed, just wet a paper towel and wipe it off... if it is thick, wet it and use the scraper to get the heavy stuff off then wipe it clean,, it isn't hard.