Does omitting "can" change anything?
"You react best under pressure. This can be an asset."
"You react best under pressure. This is an asset."
What's the difference? Is there none?
Solution 1:
In your particular example there is a difference.
You react best under pressure. This is an asset.
This states that your reaction under pressure is unequivocally considered an asset. While the first version...
This can be an asset.
infers that it is considered an asset in some set of circumstances. That's because the use of "can be" implies there are also circumstances when it "can't be" true.