I have been primarily working on gathering classes with my highest being level 37. I've been leveling them so quickly through leves, I'm afraid the materia would only be wasted. I've just been focusing on HQ gear when I upgrade.
There is never a time while levelling that you would "worry" about putting materia in gear. Materia is more something to edge out PvP gear or upgrade your Relic weapon to Novus level.
For PvP, there is a level 30 cap, and materia on your gear can definitely give you an edge.
For the Novus stage of the relic weapon, you can choose what stats you want on the weapon, but it requires a bunch of all tiers of materia to cap any particular stat. (Upgrading Animus to Novus)
On your first playthough of the game, (Getting to Lv50 and finishing main storyline) Materia binding is not something that you will need to worry about. While the stats from binding Materia to your gear would be helpful, there is question as to how much value you can get out of a piece of equipment before it's replaced from the story quest progression. (Where new gear will be coming in to help you keep near the item level required to progress.)
As you start to level your other jobs though, getting Materia infused gear will help you greatly in two ways:
Many of the Leves you'll get at this point will have you "kill X of y" or generally put you into fights to "collect x". Materia infused gear will help out in making sure these mobs get taken down as quickly as possible, so you spend less time per leve and get more EXP as a result.
Some Matria are worth more then others because they're required for quests (Like Relics) or for materials to upgrade one's relic weapons. The process of creating Materia takes a while as your gear needs to reach 100% soulbound, but a piece of gear with Matria already attached will soulbind quicker then one without it. As such, you can ask to get the "junk" resistance +1 materia attached to your equipment as well in order to roll for a better selling materia.
Note: In the previous patch 2.4, "Item Level Sync" has been introduced as a way to normalize instances and PVP matches. Materia is affected from that sync, so you will not get every point of bonus if your gear is very close to that cap.