You wouldn't track your budget in a planning tool, so why use spreadsheets to plan?
Many long-range planners are still generating their maintenance plans in spreadsheets. And while that might be fine for calculating start and end dates, it does nothing to make the planning process more efficient. The manual work involved in maintaining accurate and up to date aircraft usage data and then performing useful planning work in a spreadsheet is daunting. Add in the complexity of trying to align your plan to accommodate constantly shifting labor and parts availability, and other station constraints and it soon becomes obvious: this is not an optimized process.
Long range fleet maintenance planners face some fundamental pressures - to reduce maintenance costs and optimize resource utilization by maximizing yield, lining work on tracks nose-to-tail, planning sequential work by track and to make maintenance visits efficient. In the manual planning world, just reacting to changes in the network becomes a full-time job - a job that simply will not scale in step with growing fleet sizes. As planners become responsible for more aircraft and more maintenance visits, at some point automation becomes the only answer.
Consider the manual steps (and tribal knowledge) involved in streamlining a visit. Simply understanding what is due, what tasks can be merged, if there is skill available and where the work can be done is a complicated undertaking. And if things push to the right, it can take hours to complete the puzzle. But with automation, task merging rules allow the scheduling engine to combine specific proscribed checks into a prioritized list of scheduled checks. So, rather than setting up special visits for items such as airworthiness directives, modifications, light checks or inspection tasks, these tasks are folded into regularly scheduled service check visits. This ensures that visits are as full as possible, balancing work to ensure minimized ground time, the most efficient use of technician time and improving the yield of the aircraft.