Is it neccessary to varnish an oil painting?

A retouching/re-touch varnish isn't permanent, and will never dry - it gradually evaporates (basically). Someone who didn't know this wrapped his paintings in newspaper to send them to an exhibition - he got newsprint stuck all over them, which then had to be picked off, with great difficulty and tweezers.... Oiling out will even out dull patches just as effectively as varnish. Whether you apply a permanent varnish in due course is entirely a personal decision - I imagine most will. But applying permanent varnish too soon, ie before at least six months have elapsed, and longer if the paint is at all thick (I have no knowledge of either Krylon or Kamar varnish - a link would be interesting) runs the strong risk of destruction of the paint film by cracking. As you haven't had complaints, I assume that your varnish is indeed a retouching varnish, in which case the re-varnishing at a later stage makes sense. Most oil varnishes, if not all, are removable with solvent = a good reason not to mix soluble varnish with your paint as a medium. I've never used a spray varnish - if I did, I would most certainly take your advice to use it on a windless day: a lung-full of the stuff wouldn't be a lot of fun... I confess I don't enjoy the process of applying varnish by brush very much: it's extremely easy to end up with streaks, dull patches that you've missed, to apply it too heavily (and to get brush hairs embedded in it: which a spray, at least, would avoid).

I've looked up the composition of Kamar varnish, so far as I can find anything authoritative (so far). There are plenty of good reviews, and one very critical one. I noticed that on the USA Dick Blick store, there is very little information about the drying time required for oil paint, but the information that the varnish could be used for retouching. While Amazon has the information that it should only be used on paint that has "thoroughly cured and dried": there is a contradiction here that I'm uneasy with - oil paint certainly won't have thoroughly cured and dried in a matter of days: it takes months. I don't understand how a varnish can be described as good for retouching on the one hand, while on the other a caution is given (non-specifically, which is annoying and unhelpful) on allowing the paint to dry and cure.... This doesn't, on the face of it, make sense. I've left a question on Amazon for the manufacturers; if I get a reply I'll post it. In the meantime, does anyone else have any experience of Kamar or any other spray varnish which they could share (specifically with oil paint)?