Usually, guides on GR are practice-orientated. You learn how to do things. It's questionable whether this is a guide that exists to teach you something. I would rather say that it is an essay that will hopefully change your view on things.
There are two 'obvious' resources in RA3: Apart from credits there's also power. By definition resources are means of payment whose gathering and spending is up to you to manage. Now if we take this definition we see that it doesn't restrict to whether the resource is concrete or abstract or if it even is just something figurative.
So yeah, you guessed it, there are things which behave just like resources and they are what this guide will be about.
1. Latent credits
Units are invested credits. See them as credits that are given abilities. Of course the same applies to buildings and defense structures and whatever else that costs credits. On the other hand you can view credits as potential units. In theory credits and units are the same thing. Units are credits with power and credits are potential units.
The reason I make this equation is the following. If you waste a unit, you waste credits. If you spend credits on the wrong unit, you wasted those credits which transforms into you could have spent it on a more effective unit which equals wasting a unit - so, you can see that it can be transformed back and forth.
Let's look at examples. Training a Peacekeeper when you get attacked by Tanks is a wasted unit as it can't be used and therefore it's wasted money..... - that is fairly obvious.
If there's a situation where you have a Naval Yard and your opponent has no structures in the water, several things can happen: It is a good thing if you only built it so your opponent thinks that you perhaps have sub-surfaced naval units in the water and expanding to water would be just suicide. Noobish would be actually building those units.
This section is to teach you totry and never sacrifice a unit before it could cause an effect equal to its own value
- whether that may be dealt damage, gathered information or collected resources - otherwise it's wasted money.