RE: Qs on obarrays

[Drew Adams]

    I wouldn't recommend setq'ing minibuffer-completion-table and
    -predicate.  Those variables (plus -confirm) are let-bound by Emacs' own
    higher level completion functions, and I think it'd be cleaner if you
    did the same -- or just set your own my-completion-table and -predicate
    variables, since you're passing their values explicitly to
    all-completions anyway.

In my case, only part of which I showed, it's actually appropriate to use
setq, and I do (also) use my own my-completion-* variables.

But what you say is a good general rule, and not just for
minibuffer-completion-*, and not just when other code let-binds the
variable.