From: Bedlington, Northumberland, UK
I am writing from an Allied standpoint, but the only time I really am concerned abut prep is when I am landing somewhere. Lack of prep on a landing causes major issues of losses and disruption leaving you open to attack and nasty things happening. Other than that I always work on the basis that when I attack it will not be subtle but will be very overwhelming - so prep seldom is a factor. Prep takes ages - far longer than in real life - and is a pain. What you can do is prep for a target, get to 100% and because you switch prep to another target you can often end up with a carryover sometimes 30+ prep already for the new target but that I think is dependent on the state of your units.
In reality any sensible planning would do the if, then, and routine and nt just prep for one operation, but the follow ons as well
An unplanned dynasty: Roger Neilson, Roger Neilson 11, Roger Neilson 3 previous posts 898+1515 + 1126 = 3539.....Currently in 1945 of my sole surviving PBEM which has been running since the game came out.