Its often hard to know exactly how much fuel your lander needs to do certain things without trying it,, and if you try it on kerbin the results might not right due to gravity air ,etc.. if your like me and you love monitoring your deltaV required per stage and know the required deltaV to get into orbit,, return from mun etc,, you you may be ok,, but for a lot of less mathmatically inclined players(most of them) its usually a more trial and error approach. so making a good and efficient lander can be tedious with an hour of gameplay before you can test it and you may need to test it many many times. Enter the holodeck. extra button next to launch puts you in a selectable environment, kerbin, mun, eve, zeroG, etc, any height you want. No science points available here, not on the real map,, but in a virtual detail less "room" (like a holodeck), with blue lines so you know its the kerbals best approximation as far as they know post processing video effects could make it look like blueprints or somthing. Science points could be spent of enhancing the accuracy of your "simulator" key point here is to allow non hardcore players a QUICK and EASY way to verify a design of part of there rocket,, eg a lander,, a rover, the return rocket.. etc..