In E-Prime we avoid all senses of the verb 'to be'. This includes the words 'is', 'are', 'was' and 'were'. In doing so we aim to speak more precisely, avoiding lazy assertions of equivilence. It can prove difficult at first and many question the point of the exercise. However, it does bestow several benefits upon your writing when you adopt it.

It becomes harder to make dogmatic assertions.

When you rewrite such an assertion into E-Prime you either arrive at a more precise form of what you meant to say, or realise that you really wanted to say something else. For example, 'Bob is stupid' becomes 'Bob did something stupid' or 'Bob believes in a fallacy', or you realise you don't know that much about Bob's intelligence and just wanted to say he was stupid because you disagreed with something he said or did.

It helps avoid arguments

If you say 'Linux is the best operating system', you sound confrontational to Windows and Mac users. And perhaps even BSD users. The statement invites a confrontation by provoking feelings of attack. On the other hand, if you say 'I prefer the Linux operating system', or 'The linux operating system best suits my needs', then it will offend no-one. You speak your personal truth without the need to project it onto others. Thinking in E-Prime also helps you transcend such arguments when you see them happening, as arguments over which type of music or belief system 'is best' become seen as petty and meaningless. Many political arguments become pointless quarrels over the definitions of words.

You sound more scientific

Dogmatic assertion tends not to work very well in science. Using E-Prime doesn't guarantee scientific accuracy of course, but it does help you avoid making unscientific assertions. Instead of saving 'This experiment proves it is a particle', we say 'In this experiment it behaves like a particle.' The second statement could still contain an error, it may behave like a wave in that experiment, but the E-Prime sentence avoids the inaccurate assertion of proof made in the first statement.

You become less susceptible to propaganda and advertising

When people try to manipulate you into buying something or supporting a cause, they tend to use language heavilly laden with 'is', 'was', 'will be', 'are'. 'All X are stupid', 'Brand Y is what you need', 'C was a mistake, D will be better', 'Q is a P', 'F are dangerous and there will be a distaster if we don't stop them', 'H is the only way to stop F'. If you train yourself to be suspicious of all statements made using the verb 'to be', you quickly build an immunity (or at least a resistance) to this kind of manipulation.

Zen thinking?

One of the proponants of E-Prime that I admired, Robert Anton Wilson, claimed using E-Prime helps one achieve the state of mind that Zen Buddhism aimed to achieve. It seemed to work for him at least. :)

Here is a video of him discussing E-Prime...