Depending upon how the company chooses to report to the credit bureaus a credit card with no spending limits may be detrimental to your credit score.
If the card is reported as ?open? it probably will not affect your credit score, however, if it is reported as ?revolving? and the balance is set for the limit it could negatively affect the all-important debt to available credit ratio because it would appear that the card is maxed out.
And as an afterthought a credit card without a spending limit can also be pretty tempting at times?..
Read Be wary of Credit Cards with no spending limits.