what is the difference of doing something like:

[osc~ 220]
| [osc~ 230]
| | [osc~ 240]
| | |
|/ /
| /
[*~ 1]
| \
[dac~]

and:

[osc~ 220]
| [osc~ 230]
| | [osc~ 240]
| | |
[expr~ $v1 + $v2 + $v3]
| \
[dac~]

Both a technical and 'practical application' explanation would be appreciated, as I'm not sure what is actually going on under the hood, or how it makes a difference sound / performance wise.

Thanks

I'd imagine the latter is a tad more CPU expensive; the output is the same.

As far as the technical side goes, signal inlets in Pd have addition built-in. So if you connect more than one patch cord to an inlet, they will sum up before being processed. In fact, I believe it's actually done by the preceding objects (the [osc~] in your case) as they write their outlet audio to the same buffer, which is the inlet of the next object. Since that processing is being done anyway (they all have to write somewhere), having that extra [expr~] to do the summing is redundant.