Exactly. Ten masons working on ten tables together will produce much better work and faster than ten masons working on one table each, separately. That is, provided they have a suitable work area.
There are plenty of synergy effects. Let's say there's a process called fznrking involved in making a table. It requires a tool which is called a fznrk and which is only used in fznrking, which is a quick process and is only done on tables.
With ten dwarves in a workshop each, they'd all need a fznrk and they'd all need to, at some point, go and find that fznrk and fznrk the table and then go put the damn fznrk back until the next time they need to fznrk.
If you have ten dwarves working on tables, the first one to get to the fznrking part will fznrk his table and then, when someone else needs the table fznrked he'll go and do that for him, while the second dwarf can go off grzmbling the first dwarf's half finished table for him...
And, as was pointed out above, it doesn't make sense to build a crane in a workshop for one person, but in a workshop for ten it does. And that crane is going to save a lot of backs.
A bigger workshop means more room to work, more room for material, more room for the work piece and more room for specialised tools that make the job so much easier to do, and improves the quality a lot.
(Because if you don't have a fznrk you'll have to fznrk the table with a hjzmlb instead, and that takes freaking forever!)