It's a mixed picture how labels promote themselves on Bandcamp. There is no getting away from it, it is one of the most important platforms at the moment when new music is released. Some labels put up one track and then the whole album when release time comes around. Others by contrast make none at all available and just run the listings and personnel plus their press release and the fact that it has all ''sold out'' on vinyl and then almost passive agressively put it up and available quietly later.
Bandcamp is great as an advertising page for labels and for direct sales. It is far better than their own websites because at a glance you can see what they are doing at the moment and what they have been doing in the past if they include all their records which most labels tend to do or large chunks of it if too vast. Also, using expensive publicists does not always garner the results labels think they will and can be a gigantic waste of money.
The problem with Bandcamp at the moment is that is is stuffed with rubbish releases, people playing around putting demos up or just jokes, amateur artwork and the like, and then there is the serious stuff. So there is quality and the complete reverse all side by side. Spending time with it you realise what's what, but it takes effort and training to do all this. I guess most newcomers will be lost as they navigate specialist areas that they are trying to get to know a bit better. If it all becomes forgettable in terms of quality or the impression that the quality level is low even if it isn't then Bandcamp will have a problem down the line because serious music fans will find somewhere else to discover new music where the content is better curated.
Most major labels on the jazz side seem not to use Bandcamp (although I see the Warners associated Nonesuch is an exception) and they often instead especially if the track is high profile put up most of their releases around release date on YouTube.
There is no right or wrong approach. Often there is duplication across any number of other platforms. I think most jazz buyers want to hear something, preferably all the album, before they commit to buy. Of course some will never buy what they are sampling in generous quantity and for artists this is galling given that streaming royalties are tiny and do not sustain their work. But it is what it is and this is the reality now.
When things return to normal I'll be prioritising gigs and getting records, my preferred format is CD, via artists at gigs mainly. Tech companies I feel less affinity with than record companies and I prefer it when record labels are indie or artist-owned. Don't get me wrong the majors, especially Blue Note and big indies like ECM (distributed in most countries by Universal, and often grouped in with marketing via other Universal labels) put out quality product. But some times the slickness troubles me, the corporate style, the production-line house style quality, the feeling that artists have to conform to be on the label in the first place.
Labels do not matter as much now as they did given that anyone can d-i-y it better than ever before. Even distribution, previously the area that small artist-run labels or tiny indies were generally hopeless at, is easier now. Times are changing. The more the artist can be in control in terms of shaping their image and communicating their message and getting in touch with fans via media without too many brand identity ''middle men'' to sell their work the better.