battlefield-4
I know that opening battlepacks early can be useful if they contain XP boosts during a time when you are playing a lot, but is there ever a reason to wait?
Do attachments in battlepacks bear any relationship to which weapons you have/haven't unlocked?
Took me some fiddling but I found how to find your unlock progression for weapons. For some reason, the BF4 battlelog doesn't open this when you click on your weapon from the stats page (like it did in BF3).
To access the unlock progression of a weapon, click on soldier, then Unlocks. By default, this shows a page with all your unlocks like this:
After selecting a weapon, if you mouse over any attachment, it will tell you your progression in (X out of Y kills for the unlock). The orange bar helps too.
As for what is in the battlepacks, they are random attachments for the weapons + XP Boost from what I could see when I got them (same for my friends). The main difference from the levelling battlepacks is that the levelling battlepacks seems to give you attachments for random weapons from your inventory (even some you haven't unlocked yet).
High Value Target is a default commander resource featured in Battlefield 4. It reveals the location of an enemy to the entire team for 45 seconds, becoming available once that enemy has reached a six or more kill streak. Bonuses are awarded to players who eliminate HVTs, and to HVTs themselves for continuing their kill streaks.
Ref: http://battlefield.wikia.com/wiki/High_Value_Target_(Commander_Resource)
Best Answer
I find no reason to delay they can contain very useful attachments, xp boosts and player card emblems. Also when you get an xp boost it doesn't use it immediately. It will store it in the in-game start menu. To turn it on, (on console: square for PlayStation or X for xbox) and choose the boost you want that the hour timer will start and only be used when your in a game.
As for the attachments it was random for the guns you unlock it for. You don't have to have it unlocked in order to receive them. Side-note If you unlock battlepacks for a certain weapon it will only give you attachments for that weapon.