Dolppini: How much loot will I miss if I don't pick up lock picking either as a skill or spell on my character?
Lockpicking is a skill that you only need in situations where you don't want to attract attention (such as with shopkeepers). Attention can lead to battle, which can lead to:
* Dead shopkeepers (meaning that in effect, their place of business is now closed),
* Being targeted by the town's guards, and being shunned by the rest of the townsfolk.
Chest-opening spells, such as the unlocking cantrip, are not silent, and therefore don't offer the same benefit. And to be fair, any chest or container can be smashed open* with the proper use of a mace, axe or similar weapon (bladed weapons such as swords take damage from striking containers, so beware). So the skill is not needed in dungeons or abandoned lairs at all.
Thus, lockpicking is primarily a roleplaying thing. If you intend to join the Thieves Guild, and/or sneak into a certain mansion to steal one of the MacGuffins that moves the plot forward without getting yourself or anyone else killed, then more power to you.
To be honest, there is so much loot available throughout the game that theft only makes a difference near the beginning, when gold is still relatively scarce. What you would be stealing would be the shopkeeper's inventory, which you could then sell whatever you weren't using back to them the next day.
*To bust open a container:
1) Hit 'R' on the keyboard (or click on the shield icon, in the bottom left of the window) to go into attack mode.
2) Hold down either ALT key. This lets you target a non-living thing (such as to break down a door, or move a dead body).
3) While still holding down the ALT key, click on the chest with your mouse.
4) Repeat until success; but watch your fatigue, since swinging a weapon can be exhausting. Pause in real time to rest, or quaff a Fatigue potion if needed.
Protip: if you don't want your followers helping (because they might damage their own weapons, for example) hit the F5 key [Back Off] any time after starting the "battle".
TL;DR: Not all that much, IMO. But YMMV.