Lowering won't actually affect your score, but underwriters viewing it may base a decision, wondering about the reason it was lowered.
On the other hand, having a high limit may also make them think that you already have sufficiently available credit and can deny an application based on that.
As far as score wise goes, a higher limit is best as your utilization at any time is relatively lower. Utilization scales non-linearly with the decrease in score (40% utilization may drop your score 50 points, but 80% utilization is more like 150-200 points).
You should keep the limit as high as possible. If you ever get denied for "having sufficiently available credit", then just write an appeal letter explaining they increased it automatically, you don't plan on using it, etc.