SoundCloud and similar services need the right to present your songs - without that uploading them would not make much sense. They also want to prevent infringing existing rights (for example if people upload covers). An excerpt from their conditions:
"Any and all audio, text, photos, pictures, graphics, comments, and other content, data or information that you upload, store, transmit, submit, exchange or make available to or via the Platform (hereinafter "Your Content") is generated, owned and controlled solely by you, and not by SoundCloud.
SoundCloud does not claim any ownership rights in Your Content, and you hereby expressly acknowledge and agree that Your Content remains your sole responsibility.
...
By uploading or posting Your Content to the Platform, you initiate an automated process to transcode any audio Content and direct SoundCloud to store Your Content on our servers, from where you may control and authorise the use, reproduction, transmission, distribution, public display, public performance, making available and other communication to the public of Your Content on the Platform and elsewhere using the Services. To the extent it is necessary in order for SoundCloud to provide you with any of the aforementioned hosting services, to undertake any of the tasks set forth in these Terms of Use and/or to enable your use of the Platform, you hereby grant such licences to SoundCloud on a limited, worldwide, non-exclusive, royalty-free and fully paid basis."
The following may go a bit far:
"By uploading Your Content to the Platform, you also grant a limited, worldwide, non-exclusive, royalty-free, fully paid up, licence to other users of the Platform, and to operators and users of any other websites, apps and/or platforms to which Your Content has been shared or embedded using the Services (“Linked Services”), to use, copy, repost, transmit or otherwise distribute, publicly display, publicly perform, adapt, prepare derivative works of, compile, make available and otherwise communicate to the public, Your Content utilising the features of the Platform from time to time, and within the parameters set by you using the Services...."
I don't know what exactly they mean by "within the parameters set by you".
I use SoundClick myself using CC (creative commons) licenses that in effect are rather similar, except that I explicitly forbid the commercial use of my material (mainly lyrics), which includes public performances. The latter can (SHOULD) be handled by performing rights organizations. I find that methos to assign or define rights clearer since CC licenses are rather widespread. There is also no limit as for the number of songs you can upload.
In any case you should be aware that you have to give up some of your rights when sharing your stuff on the internet (you would have to host it on your own private homepage otherwise which would limit the scope considerably).
