Driving with a tire that has a slow leak can be safe so long as you drive slowly with it and avoid going on the highway.
A tire with a slow leak could become dangerous if it suddenly goes flat or blows out while driving at high speeds so be aware of that.
I've driven a car with a tire that had a slow leak but I drove no faster than 30 miles per hour and only drove it to the tire shop to get the tire repaired.
Tire blowouts can be serious especially if it's the front tire as it can cause your vehicle to roll over and kill you.
Never take chances with a bad tire and get it fixed as soon as possible.
As long as the tire is not damaged it's not usually that costly to have a slow leak in a tire repaired.
In most cases and in my case it was just a bead leaking and it only cost me $15.00 to have it fixed and was well worth the cost.