I do not really have much to say about the BandLab account as such. If it will allow me to continue to re-install my Cakewalk software, that is a service worth the trivial cost of having my email address etc. housed at another site which will probably be hacked at some time in the future and scattered about the dark web. Thank you, Equifax et. al.
The copyright issues with uploading content to the accounts is explained in particularly clear language for such documents. It is worth noting, for anyone who has anything of any value to post, that you are granting BandLab an enormously exploitable license, that may make your own use of the material difficult, at least temporarily. While you grant to other users licenses with various limits, which may effectively prevent them from using your work in ways you do not intend, you grant to BandLab itself pretty much every right in the music except ownership:
"Licence granted to us: By Submitting Your Content through the Services, you hereby grant us a worldwide, non-exclusive, royalty-free, sub-licensable and transferable licence to access, use, reproduce, distribute, publicly display, publicly perform, adapt, synchronise, prepare derivative works of, compile, make available and otherwise communicate Your Content to the public, in connection with the Service and our (and our successors’ and Related Entities’) business, including the distribution of advertising or other promotional material through the Services."
Just to be clear there is nothing unique about this extensive rights grab. You will find similar language on many of the music upload sites. But there is no need for all these rights just to host or rebroadcast your material back to yourself, as they imply. Further, the distinction between ownership of your rights, and a license in practice depends on how broad the license is, and what use can be made of it. As creator/owner you initially have the exclusive right to grant licenses, and BandLab does not have to have, and does not acquire, "ownership" of your work to use it. But the non-exclusive license you are granting them allows them to in turn grant that license to anyone else without your permission, and may very well allow them to publish or otherwise make money from your work without paying you anything. Furthermore, if you are planning to publish your material as a recording for example, you may find it difficult to find a publisher/record company that will not require you to grant to them an "exclusive" license, so that they will not find themselves competing with another publisher licensed by you. The license quoted above is a "non-exclusive" license, you (and BandLab, and any company that acquires BandLab and anyone or any company BandLab chooses), can continue to grant similar licenses to anyone, but once you have granted it, it is impossible for you to grant a publisher the "exclusive" license he will almost certainly want to acquire.
In fairness, this massive acquisition of rights, is moderated by a termination clause, which is often not found on similar upload site license agreements:
"Termination of Licences: The above licences which you grant to us and to other Users, will terminate within a commercially reasonable and practicable time after you remove or delete Your Content from the Services or within a commercially reasonable and practicable time after you terminate your Account, except (a) the above licences will not terminate in respect of Content which you Share with others (including in a Band) and which they have not removed from the Services; and (b) the above licences granted by you in User comments you Submit are perpetual and irrevocable."
On the face of it this would appear to give you the option of removing your content and terminating the licenses to BandLab itself, after which you could presumably grant an exclusive license to someone else if those were the only other non-exclusive licenses you had granted. The "commercially reasonable and practicable" phrase is open to interpretation, but presumably any use of your rights which BandLab was making money from, or which it would cost them money to discontinue would not immediately be terminated. Else why the odd modifier "commercially?" The exception (a) would seem to be in line with their assumption that collaborators are co-owners of material on the site. But consider that this creates a tar-baby by which someone with whom you have shared can effectively continue to use whatever rights you have licensed so long as he simply keeps the material on the site.
And there is an additional consideration in this context in that copyright law (as opposed to BandLab's license contract) typically makes a license to create a derivative work irrevocable if the derivative is created during the license term. That interpretation derives from the concept that the author of the derivative work has his own right in that portion which he produced independently, and the copyright owner of the original work would be able to vitiate that right by withdrawing the license unless the courts recognized a permanent license. So if someone sets his lyric to your music with your permission, or creates an arrangement of your music while it is posted to BandLab, you may not be able to do much if he uses it to make a hit record for himself, even if neither version is still hosted on BandLab.
So long as you understand, not just what you are granting and to whom, but how these licenses may be exploited outside of the immediate use of having fun sharing music, there should be no unpleasant surprises. But the courts can always count on business from former friends/band members who have fallen out over who controls exploitable copyrights. Consider the implications of band members/collaborators who are strangers scattered across the a global network of various laws and jurisdictions. Heed BandLab's advice to have a written contract, not just the BandLab terms of service, that clearly explains how those rights will be allocated and controlled, if you think anything worth fighting over will come of your collaboration.