Years ago, when I worked at In Focus, we had a layout guy: Tom. I don't remember his last name.
He was a wizard. With one hand, he could be punching key codes so fast I could barely follow him, with the other hand, moving the mouse around like crazy, all while talking to me.
These days, it's pretty common for engineers I deal with to have lost that resource. The layout specialist is gone and the design engineer has to do the job. In general, I would say that they don't like it, nor have they all been trained on what makes a good, manufacturable, PC board.
Multi-sourced, and a nice attribute of these configurable logic gates is their Schmitt inputs. This allows them to be used as various types of timed pulse generators by placing an RC network at one input.
elizabethsimon: ATF16V8CZ are 5V and have been easy to source from multiple distributors. At $1-2 they are cheap enough, sink 24ma, source 4ma. Buffer with a high current octal ttl part for more drive.
Not to say they will be around long, EOL is striking a lot of 5v PLD parts. One of those parts worth buying up a long supply ... cheap enough, and worth it long term.
This is a good philosophy for NEW designs. Unfortunately, there are some cases where it won't work.
It's becoming difficult to find PLDs and most newer CLPDs and FPGAs are not 5V tolerant. So when I had to add a fast (<4ns) buffer to use as a level translater from 5V to 3.3V, the only thing I could find that would work were some single gate parts.
I recently had to replace an FPGA that became obsolete with a newer part. Not only were the pacakges and pinouts incompaible but since the new part was not 5V tolerant, I had to add buffers (with logic to switch the buffer direction) that weren't required in the original design.
This is the kind of thing that happens when you work for a company that's still building products designed when almost all logic wa 5V
There are single and double "definable" gates from several suppliers. They cost pennies and are SOT-23 in size and 6 pin micro BGAs. You can define their gate "function" at the time of installation (http://www.ti.com/lit/ds/symlink/sn74aup1g57.pdf) I am sure they are cheaper, lower in power and smaller than any PLD option. Heck, why use a PLD? why not a micro controller ( they are certainly getting very ,very small, fast and very , very cheap).
I know a lot of companies that would prefer they didn't have to keep both C/C++ programmers AND programmers that work exclusively in programmable logic tools. I know a few C/C++ programmers that would like to take back control of that programmable block - without having to learn another tool set.
We have so many options today.
I understand why you may want to have some excess / spare circuitry because the product has not been completely defined, may want some design re-use (modularity) or as a simple CYA (cover your A...) for the unexpected.
Lower volume products (less than 5K/year).. mmm OK, sure. makes sense.
Often flexibly and design re-use trumps cost/space/power choices.
But.. I wouldn't assume this to be a "best" practice to be recommended to others.
Henry Ford's definition of a engineer: "A engineer does with one dollar what any fool can do with two dollars".
I've used single-gate chips recently. They're very nice for I/O modules where you need the drive current and/or protection you can't get from a PLD. They're also nice as part-stuffing options, for example when you have several different kinds of copper and/or fiber interfaces and some need active-high signals and some need active-low.
NXP has some versatile 6-pin configurable logic gates. You get different functions by connecting your signals to different pins and/or strapping pins to +V or ground. This lets you get a lot of different functions without stocking a lot of different parts.
Think_j: I think I would still use a low cost PLD for a single gate, simply to have the extra unused outputs and inputs available on the board for ECO's or semi-custom variations of the design that can do some signal management of inputs/outputs as needed. It's much easier to stock PLD SKU's, than a wide assortment of TTL in the long term. Every company has different views and requirements on this.