Rogue firmware fix some bugs and add features to base firmware. Not everybody see that bugs, if you only use emulator with few games probably never have a problem. If you code your own games, surely you will face some of them.
In system, this firmware fix some problems with original filesystem and stuttering when booting the console. Have some libraries updated, battery accuracy updated in kernel, add support to usb hid (you can connect keyboard and mouse), wifi drivers, new filesystems (fat32, exfat [read faster, works in win, mac, linux], ext2-ext3-ext4 [read faster, works only in linux].
In apps, it have fixed buttons for rg350 in Glutexto, Dingux Commander, GCW Connect, and any visual improvement. Gmenu2x have a lot of improvements, show of battery percent, new previews system, a reader, possibility of edit names and icons of apps, block screen pressing power, selection of over-underclock to save battery...
And some old apps have been replaced for a new ones: Clock, RG350 test (test buttons, joysticks, sound, vibration and cards). And a new one: Scriptrunner, allows you to run your own scripts or use some installed, for example, you can format extern sdcards from the console.
If you like test new things you can try new firmwares replacing internal sdcard (save the original as a backup), that can not break the console. If you don't have problems... don't do it. xD
I hope this resolve some of your questions.