It limits what peripherials can be attached. For instance, single graphic card uses 16 PCIe lanes, so having only 28 lines supported by processor makes it impossible to have two GPUs in SLI mode (ok, not impossible, because motherboard chipset can add some lanes, but performance will suffer)
NVMe SSD drives also use some lanes (typicaly 4), and you might want two of them in RAID.
NVMe SSD drives also use some lanes (typicaly 4), and you might want two of them in RAID.