Both keep a bot online when your computer is not. The difference is how much machine comes with it, and most bots do not need one.
What bot hosting is
A container with a runtime, a web panel and your files. You upload the bot, set the start command and press start; the console shows the output live, the file manager edits a config without an SSH client, and the process restarts on its own if it exits. Our plans run 512 MB to 4 GB of memory and 50% to 200% processor, where 100% is one core, with a weekly backup.
What you do not get is a shell, root, or an operating system of your own. You cannot install a system package, run a second unrelated service or open an inbound port. For a bot, which makes an outbound connection to Discord and listens for nothing, none of that is usually missed.
When a VPS is the right answer
- The bot is not the only thing. A dashboard on a domain, an API other services call, a database you want to administer: that is a server's work.
- You need a system package. A native library, a binary the runtime shells out to, a specific build of something.
- You want inbound connections. A web interface, a webhook endpoint, anything with a port of its own.
- You want the whole stack under your control. Some people simply prefer it, and that is a legitimate reason as long as you are also taking on the patching.
Sizing, which is the question people actually have
A small command bot runs in tens of megabytes. One holding a member cache for busy guilds needs hundreds, and that grows with how active the guilds are rather than with how many there are. Music and voice are a processor question instead: the stream is decoded and re-encoded for as long as someone is listening, so a music bot wants the processor column and a moderation bot wants the memory column.
Cost, plainly
Bot hosting starts well below the virtual server range, because you are renting a slice of a machine with a panel on it rather than a machine. If the bot is only a bot, paying for a server you then have to administer is paying twice: once in money and once in the evenings you spend patching it.