Once again, this misinformation rears its head. This was discussed at length not long ago when more than one professional explained how it was used when assembling joints on high current busbars and other applications.
Yes Vaseline is an insulator so if the OP and you wish to substitute terminal dressing that looks exactly like red Vaseline or terminal grease (as issued to the UK armed forces) then fine, but they are all insulators in their own right, but that is not their purpose.
If no terminal dressing is used then and very slight leak of acid or acid fumes through the post to cell lid seal will penetrate the small gaps between the post and clamp/terminal and create a very hard, black oxide type coating that really is insulating. This works its way across the whole surface and the engine will fail to start, giving machine-gunning and/or other "flat battery" symptoms. Negative terminals are particularly affected by this. If the dressing is cleaned off, all will appear well for a time, but the time period before a problem occurs is likely to be much reduced.
Even now with much better post to cell lid sealing one still sees the area around the post, terminal and lead badly corroded with typically white, yellow, or bluish growths. This is normally the result of acid/acid fume leaks, so it can still be a problem.
Just because you or I have an idea fixed in our minds does not make it correct, especially when it is contradicted by others with similar training and experience. The OP can take whatever advice she chooses, but dressing the terminals or not will make no difference to solving the problem, it may make the time before the next problem shorter