Optimal route planning that takes into account vehicle capacities for deliveries (and/or pickups), both from the depot and intra-route pickups and drops-offs, can vastly improve efficiencies at the depot or warehouse leading to time and cost savings across the board.
Route planning & management relies heavily on time, but not always in the way you might thing. Delivery planning software has to lower an entire fleet's overall cost to company - even if this means increasing the time and cost of individual vehicles for the greater good. As the old adage goes, "time is money" and saving it is not always straightforward.
Generally, there are two types of time constraint that go into route planning:
Constraints on vehicles used for pickups and deliveries is a hard fact of business. Some items might need to be kept in a cold chain environment. Others might require a forklift to be moved on and off the delivery vehicle. Managing any type of constraint on deliveries while minimizing costs is vital for virtually every transport related business.
Precisely what type of constraints your business encounters is often going to be fairly unique so it pays to have real flexibility when it comes to optimizing around these constraints.
Real world route optimizations must take into account a range of costs associated with your fleet of vehicles in order to accurately portray optimal solutions based on the specific characteristics of that fleet. Any system that only takes only distance or time into account (but not both) is not going to be able to calculate the best possible solutions because it is ignoring half of all your cost generators.
Optimizing routes is hard. Especially when you have to produce solutions that businesses can use in the real world. This means taking into account what individual vehicles can and can't carry. After all, there's no point in letting one vehicle visit all the locations on your delivery schedule if it only has sufficient carrying capacity to visit one or two stops at a time.