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Google it, jk
Prints can stick better resulting in better quality
Because prints stick better, vibrations are not as much of an issue
Can help in removing print w/o damage because it hardens forcing it off (if that matters to you)
Despite what some people say I recommend it for PLA and ABS because both LOVE to warp and ruin your 20 hour print

Any residue can be an issue
It picks up residue from glue or tape and can affect print
One more thing to worry about
Too hot and you can get prints to sink into the bed and mess up the print or get "Elephants Foot" which is a wider bottom layer, this can be an issue for parts that are put into one another
Depending on printer they have issues and some will actually STOP a print if there is an error with heater bed

And I also wish you good luck on your endeavor of building your 3D printer out of a 3D printer!