In reply to Huygens.

Most cheap web hosts offer a system for tracking resource usage. The most important one to take notice of is your CPU usage. Consistently high'ish usage is okay, but it's big spikes which can cause serious problems. If you have a flat CPU usage below their limit, then you are unlikely to get suspended. But often, you can have a fluctuating usage, which on average may be low, but as soon as you spike, you risk bogging down the whole server, and this is what will get your arse banned ASAP.

That PHP memory limit is only on a per page basis. You shouldn't generally need to adjust it, and if you are, then that's probably a sign there is something wrong with your site, perhaps a plugin which is sucking up more memory than it should. Or it could be that your host provides sucky defaults.

You can solve all of this by getting a VPS. With a VPS your site will just run slower than normal, and you won't get banned.*

* actually, you can theoretically get banned, but I've never heard of that happening in normal circumstances.