Sorry I do not get it why a spell requiring concentration (Haste , GoI) could be stored in a demiplane in a concentration-less form and retrieved from there at will?It's a bit more than convenience; with a Glyph of Warding the spell ends if the glyph is moved more than 10' from where you place it, it is dispelled. So that means that while in principle you can use it to maintain multiple concentration effects (or just "pocket" a spell to cast later), that only works if you are going to be in the same location at the time you need to use the spell, which, since the Glyph takes an hour to create, is a pretty big restriction that will usually prevent you from using the trick in combat.
But with demiplane, you can use an action and an 8th level slot to get, say, a concentration-free Globe of Invulnerability and a concentration-free Haste, say, provided you had some downtime and 200gp beforehand, allowing you to still use your concentration on, say, Animate Objects; so you have big offense and big defense at the same time.
I mean, given even a single day of downtime, sufficient gold, and access to demiplane and plane shift, you could prepare for the BBEG battle by loading up your demiplane with, by my count, after factoring in the need for plane shift to get out, and the need to upcast glyph to match the spell level you're storing, six buffs (at 20th level) ranging from 3rd to 6th level spells. So you could stack, say, Globe of Invulnerability, two conjured elementals, greater invisibility, haste, and fly, all concentration-free, and all cast with a single action and 8th level slot on the day you trigger them, and still Wish yourself a Simulacrum and cast Animate Objects, all by round 3.
Do you folks use a different set of rules than me? With haste it says nothing about not needing concentration anymore if cast at 8th level. Guards and wards needs an everyday casting for a year to become permanent (and I wonder if its effects are not dispelable still?) else it is 24 hours.
For the Glyphs, yes you could cast them on objects and get some explosion or other thing if you move those objects up to a maximum of 10' so this seems pretty impracticable, better cast some offensive spell with your 8th level slot so you stay out of melee.