Some well-meaning but harmful advice

Can you figure out why the following statements are wrong? They are all well-meaning pieces of advice on the topic of capacity management. I'm sure you have heard them, or even given them.

Regarding cluster RAM:

• We recommend a 1:2 overcommit ratio between physical RAM and virtual RAM. Going above this is risky.
• Memory usage on most of your clusters is high, around 90 percent. You should aim for 60 percent as you need to consider HA.
• Active memory should not exceed 50-60 percent. You need a buffer between active memory and consumed memory.
• Memory should be running at a high state on each host.

Regarding cluster CPU:

• The CPU ratio in cluster X is high at 1:5, because it is an important cluster.
• The rest of your clusters' overcommit ratios look good as they are around 1:3. This gives your some buffer for spike and HA.
• Keep the overcommitment ratio at 1:4 for tier 3 workload.
• CPU usage is around 70 percent on cluster Y. Since they are User Acceptance Testing...