Sometimes it can be frustrating when you've got that perfect idea for your next tattoo and the artist you want to work with has closed their books for a while. The reason artists have to do that is to get caught up on their workload and stay focused on the clients that they've booked appointments for currently. It's not uncommon for tattooers to do multiple consultations per day, meaning that each day they are filling slots on multiple days. This becomes an exponential endeavor and can easily become overwhelming.
Having a long waiting period between the first meet-n-greet and the actual session can also produce frustrations. If you're on the books for 6-9 months after your consultation how many times are you going to overthink the idea? By the time your session date comes around you might have to have another consult to refresh both your memory and your artist's. Although it may be annoying not getting in right when you want, it is way more beneficial to not have a huge gap between the actual tattoo session and that awesome initial meeting when you were super excited and really clicked with your tattooer and your idea.