What do you use Tasker for?

[CranialBlaze]

How do i set wifi to switch off when it disconnects from a wifi network?

Set up a profile to check for not connected, with a task to disable wifi. You may want to put a delay on that as well as it would not benefit you if the WiFi drops for a few seconds and now it's off.

 

[CranialBlaze]

Is it not better to leave Android to manage the RAM by itself? As far as I know, clearing memory has little benefits.

It actually has zero benefits, it's a detrimental action in the vast majority of cases, Android memory management is top notch, so clearing it increases can usage and in turn decreases battery life while also decreasing performance.

Only apps regularly used take up any real memory, the rest are deprioritzed and cleared out based on need. So if you launch a new app and memory is needed, or an idle app is returned to active status.

Androids operate optimally with less than 20% free ram.