I do seasonal maintenance for many people and I can tell you the most obvious time and money waster is the wrong plant in the wrong place. The most noticeable culprit, shrubs that need to be pruned regularly to keep their size in check. At one home, a huge photinia was pruned by the gardener weekly (!), probably costing the homeowners $1000 per year. Another homeowner had a new expensive swiming pool installed with specialty hardscaping and a pergola. Then, the plants were installed ... Feijoa sellowiana, or Pineapple Guava, which normally grows 18 - 25 feet, surrounded the hot tub, and Pittosporum tennuifolium, which again grows really big, under the windows. This homeowner, btw, likes things tidy, ahem. She would not want a wild, overgrown garden! So, it's now "Pruning Time - All the Time!" at her house.
Look at all the squared off shapes and globes, especially in commercial landscapes. Why not plant something that is the appropriate size and let it be, like this blue fescue planting?
If you have trees or shrubs that you have to continually hack at, or trees or shrubs that routinely "get out of control", why not pull them out and find an appropriate plant. There are lots of them out there. A tree or shrub that is the right plant for the right place is one you'll get to know and appreciate thru the seasons for its own unique characteristics.
Note: sometimes people like to putter in their gardens and this is cool, sometimes people like plants that require specialty pruning or care(veg gardens, topiary, roses, grasses (yum), whatever). I know I do. I'm just tired of seeing ugly pruning jobs and want people to have gardens that speak more to their hearts, and where time spent taking care of the garden is a joy.
Call me if you need help picking your plants!