Personally, I thrive off of maximizing my lesson/review count, as, with my learning speed and needs, I feel listless and underwhelmed when I have less than 74 items. I intentionally delay my use of KaniWani until I have near 1200 reviews and then stack them intentionally.
The function of the SRS system is thus: how many reviews you have at once is determined by how many lessons you do at once and by how much you keep up with your reviews. The amount of time between each review is set and staggered in a way to optimize your ability to remember it. If a user is consistently going multiple days without reviews, the effectiveness of the SRS system is reduced
Vacation mode will halt your reviews if you need to take a few days away from WaniKani. While it seems wasteful at low levels, since it also slows your progress through WaniKani by delaying critical reviews, once you have all tiers of content (from Apprentice to Enlightened), using vacation mode when you are unable to review will help prevent the previous content from creeping back into your reviews with your new content as easily.
I do think it would be interesting to have an option to slow down/speed up the intervals between each tier, allowing for a more relaxed or more stressful work load at the preference of the user, but that also risks the integrity of the SRS system (those strong in short-term memory would have less long-term retention in shorter queue times and those using longer terms have would risk accuracy due to susceptibility of forgetting between reviews).
Like @acm2010 said, try managing your lesson consumption. My personal restriction for myself is to only complete 50+ lessons if I intend to finish the level within 8 days and to subtract 5 lessons from 50 for each subsequent day after 8 I intend to remain on the level. Of course, the lower your accuracy, the more divided your reviews will become, so, if you’re willing to endure the masochistic practice of forcing yourself through massive numbers of reviews, it’s likely your queue will natural split up between those words you remember well and those you don’t.