You're probably thinking of morph injections. That's not what ExP is. ExP was solely to enable morph injection in Poser 4. Morph injections do actually save on system resources. ExP does not. It's actually more resource intensive than just using Poser's Binary morphs.

DAZ's ExP system wasn't to accommodate low end systems. The entire figure still has to load for the figure to be loaded. ExP was created because Poser 4 didn't have a way to add morphs channels to an existing figure. At least that was DAZ's story when they introduced it with V4. Except the ability to add channels was added to Poser 5. V4 didn't come along till poser 6. DAZ just ignored Poser's innovations. DAZ continued to ignore Poser advancements. That created the illusion that Poser lacked innovation with their products, DAZ also never supported Keyed Dependencies, Material collections (Preferring the Mat-pose hack), binary morphs and probably a bunch more I've repressed the memories of.

So ExP was a work around for a missing Poser feature that hadn't been missing for 2 full versions..

Binary morphs were a more complete solution to the low end system problem. Unfortunately bugs in PMD when introduced lead to it largely being rejected. Binary morphs have a super power that few people know about. When a figure with morphs in PMD format is loaded none of the morphs really aren't loaded. The actual morph data isn't added to the scene or system memory until you actually use the morph. The biggest advantage was that you didn't have to stop and load a morph injection if you needed another morph pack. For a PMD figure all you needed to do was spin the dial. The morph data is automatically read from the PMD in real time.

P.S. A Poser style morph injection is 2 files. A PZ2 and a PMD. A DAZ morph injection is thousands of files.