In some countries (like the UK, which is where I am) an employer must make reasonable adaptations to your working environment where necessary to account for disabilities - where the notion of a disability can be self-defined. I don't know whether you'd consider Asperger's to specifically be a disability (not being familiar with it myself) but it would seem to be constructive to treat it as one for these purposes. Of course, they can only be expected to do this if they know about it.
What reasonable adaptations would be appropriate for you would be best defined by collaboration between you and your employer. Perhaps (I am clutching at straws here because I don't really grasp personally what life is like for people with Aspergers') policies concerning internal office communications that state generally-useful principles (like keeping the use of idioms or sarcasm to a minimum) that would be especially helpful for you, would be a practical step to take. Adherence to the policies should be monitored by somebody in the management chain and friendly reminders issued where necessary.
You can be pro-active about this if your workplace runs something like a PDP (Personal Development Plan). An example would be for you to review recent situations that you specifically found challenging (or conversely, ones that you thought went well) with your line manager and where possible, agreeing a strategy for you to use in similar situations. Again, this can only happen effectively if your line manager knows you're managing a specific condition of yours.
It is also worth noting that in most developed countries, treating someone disadvantageously because of a disability is illegal. If you feel you've been treated unfairly, it would be easier to distinguish whether or not this was intentional discrimination if it's unambiguous to everyone that your Aspergers' is a known quantity.
So to answer the question - I think the benefits of telling your employer greatly outweigh the disadvantages, unless there is something specific you're worried about.