All items have a skill involved in merging them. It is often alchemistry for reagents, potions and powders, giving the thaumaturge the advantage. If the work is done in front of an alchemy bench, the thaumaturge gains a huge bonus to all merging that requires the alchemistry skill. This means that if you find an alchemy lab early in the game you may be able to do all sorts of merges of alchemical ingredients you don't necessarily have the skill for yet. With the bonus you can do the merges at the alchemy bench. I have already stuck one of these in the back of Trimestes shop as you head towards the Museum of Magic, so once you buy a ticket back there you will also be able to use the bench.
Other items may require skills like Nature Lore to merge and at a hearth you will soon find that the ranger and thief will get a bonus here to merge items like these. At the forge the Thaumaturge gets a skill bonus for metallurgy and can also forge and sharpen items individually, improving their qualities substantially in combat.
As a general rule, whatever the class may be, if there is a skill marked as getting a bonus at that kind of workshop station (forge, hearth, shrine, alchemy lab) then the bonus is applied even if they only have one skillpoint in that skill. Obviously, a 25% bonus to 1 skillpoint still yields 1 skillpoint but in principle they get a minimum extra point of 1 applied to that skill in the merge.
The shrine offers a lot of special merges, permits templars and clerics to bless weapons (permits them to hit magic creatures) and heals special conditions when the party sleeps at that site.