i always replace. tubes cost me $4 at the LBS. Patch kits cost around the same, maybe slightly cheaper. Patching takes time, honestly not much, but when I'm in a hurry to get home the difference in cost between patch/tube is so small that I honestly don't care.

Since March I've used 3 tubes (and two were right at the beginning when I was using an incorrect tire pressure) for a total of $12 over 1000 miles on my bike. Honestly thats the cheapest thing I've encountered on the bike!

Patch kits may cost around $3, and I used to buy one after every flat anyway becuase the open glue tube might not last the month or two until I get another flat.

So I just replace. That way it saves me some time on the road.

I do carry a patch kit and spare tube in my pack just in case I get multiple flats. And I always offer help to those stuck on the side of the road.