Finding the right climbing shoes is a balance between comfort and performance.

Your first pair of climbing shoes should be comfortable and sit tight, but without being uncomfortably so. If they are not tight enough, the support for the foot and the feel of the wall / holds can be diminished to a degree that impedes your climbing. If the climbing shoe is not tight enough around the tip of the toe, the support for the toes may not be adequate when you stand on a small hold. The shoes will bend and you will lose your footing. The tighter the shoes are, the easier it will be for you to stand on very small footholds. But if they are too tight, the pain can ruin your entire climbing experience.

If you are mostly into bouldering, you may want to buy a pair of climbing shoes that sit a little tighter than you would otherwise like for rope climbing. During bouldering, one does not typically wear the climbing shoes for as long. When you are on the boulder problem, you have the climbing shoes on and when you are not climbing you can either pull the heel down or take them off completely.