It depends on what your hazards are. I ride on one of the most junk strewn roads in America. Goatheads are the LEAST of the problems. I finally settled on Schwalbe Marathons (both Armadillos and Gatorskins proved less than satisfactory), with "thorn resistant" tubes AND slime. And I *STILL* manage to get the occasional flat. What the slime usually does is allows enough air to stay in the tube to get me to my destination, where a "real" patch can be applied without having to stop on the side of the road. I DETEST having to stop on the side of the road. I also DETEST flats - I haven't had a flat tire on any of my cars in 25+ years, I expect my bicycle to be the same.
So it really depends on hazards and your priorities. Slime has gotten me home on several occasions - totally worth it as far as I'm concerned.