To a very large extent it depends on numbers, however in broad terms it means that the Russians have lost a huge 'safe area' from which to stage their logistics and Command & Control effort.
Uptil now, that meant they could operate large, static supply dumps, and HQ's, beyond GMLRS range, that's about 90 miles from the front line. So they could have a big ammunition supply hub on a railway line about 100 miles from the front line, and truck it in from there. Now the Ukrainians have Storm Shadow, that railway /truck transfer point is 300 miles from the front, not 90. Its akin to supplying everything Glasgow needs, by lorry, from the rail head at Carlisle. Now change that to supplying everything Glasgow needs, by truck, from the railhead at Worcester.
That means a huge increase in their dependence on, and need for, trucks - and guess what they don't have?
It also puts the Russian Black Sea fleet home port, and all of Crimea - it's bridges, it's airfields, it's HQ's - in range, when they weren't before.
For HQ's, it means both moving about a long more (which is a gigantic pain in the arse), and making a lot less electronic noise (radio traffic), as well (ideally, because of the above) as moving another 200 miles from the front. But there's a problem here for the Russians - everything about how they fight shows that HQ's have to be right up the arse of its fighting formations or nothing/chaos ensues, and that their poor training ethos, and their 'top down ' command system, means that nothing happens without a constant stream of instructions.
Rather like my children, the Russians work well when under constant supervision and cornered like a rat in a trap.
It also means they now have to protect a vastly larger with the same number of air defence assets.
It could be a Chally 2 moment - it opens the floodgates: both France and Italy operate Storm Shadow (SCALP on France's case, but it's the same thing), and the US ATACMS missile, which the Ukrainians have been asking for, but the US denying because they think it's escalatory, but has a shorter range than Storm Shadow, could be on the way after this. Same principles would exist, just in far greater density.