Telect recommends a best practice of using one fuse for each panel — whether DSX or otherwise.
The concern with not following this recommendation is that you may need to over-fuse to satisfy the load of two or more panels. That puts each panel and personnel at risk.
When dealing with DSX panels which draw current for only alarm or status LEDs. Most panels with just LEDs draw very little current — about 7 mA per LED — but the power bus feeding them can tolerate a lot more. In addition, the smallest GMT fuse rating of choice is more like 600 mA which would “seem” to allow for much more wiggle room when it comes to load. (In addition to that, it is likely that not all LEDs will be lit at the same time.) But when you start to add up the load, for example, a single panel of 48 LEDs drawing about 300 mA (max.), you enter a grey area when adding a second panel to the same power feed.