It depends how you ride.

Basically a really bald tire may be close to the point where the canvas tread shows. If so, you have much less traction at those points. Watch out for curves and sudden stops!

A really bald tire may suffer from a blowout on something minor like an uneven sewer grille.

When the canvas shows, it's a blowout waiting to happen. Beware especially of any bulges.

A blowout on the front tire is a good receipe for disaster (i.e. crash). It's less hazardous if it happens on the rear wheel, but still at fast speed, it's something I prefer to avoid.

When it happens -- and sooner, rather than later, you will have to walk home or repair the tire on the road. Why not change it at home now?

Regards,