Is its purpose to download things for you in their server and then you download from them faster?
Yeah. I'm not aware of any limits too.
When used with stremio orkodi addons it lets you stream videos directly from their servers, without the need to download the file
You cannot upload. So no use as personal cloud. Popular torrents are already cached on their servers so no need to wait. Other plus is you probably max out your line speeds. Traffic is SSL encrypted, no need for vpn