Which is cheaper regular preventative maintenance or repairs when troubles arise?

I used to do roof maintenance for a local business.
Periodically I’d repair the flat roofs.
The owner wanted a regular schedule, every third month, their two flat roofs being checked and any areas that were suspect being repaired.
This to prevent the ceiling tile and sheetrock and insulation from being damaged.
He retired and one of his sons took over the business.
This son wanted to be efficient and run the business economically.
Each time I came to check the roofs, he wanted to approve every little repair that I deemed necessary.
That is okay but then he demanded to know how long each job took wanting to be cost efficient I’m sure.
Surely his minimum wage employees could do what I was doing and do it so much cheaper.
So he decided that I charged too much and that he’d not call on me in the future.
We saw each other in a store parking lot on Tuesday this week.
I inquired about the roofs.
They’d had a leak this past week during the rain showers that occurred.
I asked where and he told me that it was just next to an area I’d build up and had repaired the last time I was there.
Also he told me that in March a crack had developed over the office and some ceiling had fallen down.
My last statement date was July 18, 2014. I’d charged $127.00 for my time on the roof ($100 labor / $27.00 materials).
The intervening time was 7 months with no check ups.
Replacing the ceiling was cheaper.
As soon as he told me of his woes I thought, “an ounce of prevention” and in this case it would have been worth more than twenty pounds of cure. But I didn’t say so, I ┬ájust commiserated with his plight.
So I ask you again.
Which is cheaper? Prevention or cure?

hafen roof 9