A credit inquiry is not good for you because every credit inquiry pulls down your score by a few points. For most people this does not impact their score at all because five or six points can be covered in pretty good time, especially if your credit is approved.
However, if you get rejected, you tend to apply again and then if you get rejected again, these negatives can add up pretty quickly. That is where it helps to get an idea if you will be approved for credit or not.
Most credit card issuers do not clearly state what kind of FICO scores are needed in order to get approved by them. So it can be a little difficult to find out before applying if you will get approved or not.
WhoGaveMeCredit is a good resource which has a list of credit cards and the scores at which they were either approved or rejected. You can see the credit card issuer, state in which it was issued, score at which it was approved, date and the credit limit.
So for example you can see that Chase Platinum was issued to someone with a Trans Union credit score of 685 with a credit limit of $200 on 07/04/04 in the state of Arkansas.
This is a good resource and while it is not completely exhaustive it is better than have nothing to go by.