Generally H-axis washing machines should be loaded to full rated capacity by weight. That is for normal cottons/linens if machine is rated for 15lbs that is what loads should be. Under loading H-axis washers causes all sorts of issues such as vibration during extraction, making it difficult for machines to properly distribute loads for extraction.
If machine cannot balance loads properly things vary by programming but usually it means washer will stop and attempt to rebalance load. Try spinning again and if same result will repeat process again. This may go on for a few more attempts until washer either won't spin or will do so at lower speed. Either way all that pfaffing about with aborted and repeated spinning takes up time.
Constantly under loading or otherwise causing conditions are out of balance during extraction is hard on washer. This can lead to issues with bearings and support suspension system.
Mind you there is a world of difference between say 15 pounds of terry cloth bath towels and wash cloths versus bed sheets and pillow slips.
You have to take into account drum volume in relation to capacity. A properly loaded H-axis washer will tumble goods from 2 O'clock to 8 O'clock
Terry cloth and some other fabrics will greatly compact down once wet. Some weaves of bed linen and other textiles may not.
You can see even with a Milnor divided cylinder washer operator loads each pocket to full weight/tub capacity.
When washman loads machine you can see linen has compacted down quite a bit.
Then of course there are diapers...
Commercial/industrial laundries long weighed wash loads and most still do. IIRC early on in semi-automatic and fully automatic washing machine days it was suggested laundresses, housewives or whoever was doing wash should weigh loads to ensure weren't over loading or under loading certain machines. I *think* this may have been with early Bendix or other front loaders.
SQ washer that appears "stuffed" when loaded, but notice how things compact down when wet.
Much smaller load in SQ washer:
https://www.youtube.com/watch?v=uJFHsEI7XOI