Is the phrase, "Use commas sparingly" a valid piece of advice?
[Edited:]
This process makes use of commercially available software to read the data files, and custom software to convert the files to a different data format.
I agree that this comma is a matter of choice. It isn't really necessary, and I'd definitely not use it in short parallel sentences with ellipsis; but in longer ones such as this most respectable authors would feel free to add a comma if it improved readability. I'd use one here.
The organization does not regulate the data products it receives, and the software application cannot always read the data due to errors resulting from different vendor implementations.
There is more or less consensus among style guides that a comma is required between independent sentences without ellipsis. Depending on context, a semicolon might be used here by some instead.
The use of commas is a very complicated and ambiguous matter. The comma in your current title, Is the phrase, “Use commas sparingly” a valid piece of advice?, for example, would be recommended by some style guides but advised against by others. It would help a great deal if you posted a few example sentences that you'd like advice about. A few general statements:
The use of commas has decreased over the past centuries; most people probably use fewer commas now than in 1900.
The adage "use a comma whenever you hear a pause" is not reliable: yes, there is a relation between commas and pauses, but it is rather vague and irregular.
As a very, very crude rule of thumb, I'd say it is usually better to skip the comma when you are in doubt.
Reading a modern style book's chapter on the use of commas may be a good start.
Expanding/non-defining relative clauses (my house, which I bought last year, is fantastic) are usually separated by commas, whereas restrictive/defining ones (that's the house that I bought) are not.
Whenever you separate a phrase or word in parenthesis by commas, make sure you use commas at both ends, not just at one end or the other (unless of course there is a heavier punctuation mark where one of the commas would be).
Don't separate the main verb from its essential complements by commas unless some other reason forces you to do so.
Some writers get a bit comma-crazy using the "punctuate by breath" method and they should indeed be reined in. In some academic and scientific writing, authors lean on the passive voice overmuch and add endless qualifications to statements, resulting in comma proliferation.
So... if the intent of the adviser in this case was to actually express the idea that one should write clearly and cleanly, and that comma over-use is correlated with bad writing, then I guess I can give it a pass.