Pro: You know if a guy actually likes you
You know how a gentleman treats his girl and you won't allow a guy to treat you otherwise. This eliminates a lot of the guesswork for figuring out if a guy actually is interested in you.
Con: It might be harder to find guys to date
The fact that you have expectations for how you should be treated makes a lot of guys lose interest, and sometimes that's not the most fun.
Pro: You miss out on a lot of heartbreak
If you start out with a guy who has good character, you're less likely to endure as much heartbreak as you would have if you gave your heart to every Tom, Dick, and Harry.
Con: You get accused of being too picky
Now there's a difference between being too picky and having standards, too picky has to do with superficial things like eye color, height, the type of car they drive. Having standards is about who they are as a person and how they act towards other people. Sometimes people blur the line between those two, though.
Pro: You won't have to second-guess yourself
As time goes on, you begin to see flaws in people that you didn't see at first. If you only choose great guys, you don't have to second-guess whether or not they're worth your time and emotional energy.
Con: You regret rejecting some guys
Sometimes we make mistakes and overthink, and that leads to us missing out on what might have been a great relationship.
Pro: You hold yourself to a high standard as well
When you expect more of those around you, you also need to have those standards for yourself. You become a better person because the people you surround yourself with also hold you to a higher standard.
Con: You come on a little too strong
You know what you want and you aren't afraid to lay it out there. Sometimes that can intimidate even the guys who do meet your standards.
Pro: Your relationships aren't a waste of time
Time is one thing you can never get back, but if it's spent with the right type of people you wouldn't want to get it back anyways.
Some people might disagree, but the benefits of having standards will always outweigh the possible costs for me.