In the "New Traffic Shaper - What works…" 2.0-specific tread ermal posted an explanation with this details: @ermal:

1- A packet is queue only when going out an interface.

@ermal:

…this is the normal flow of a packet on pfSense for teh shaper. Remember the queue would be enforced on outgoing:
...
3- [packet] goes outside WAN interface
4- it matches a rule with a queue [it's the very fist place where a "queue" is mentioned - V.]
…
6- packet goes... out of WAN (gets queued on the WAN queue)
7- response packet comes in on WAN
8- matches the previous state created and finds a queue has to be attached
9- marks the packet with the queue
10- packet goes ouside LAN interface
11 - it matches the state created previously, since there is no queue it does not take any action
NOTE: this means that the decision taken on WAN for queue still prevails
12- it goes to the queue marked since it came in on WAN (if it can find it of course)
13-finally… gets queued on the LAN queue

and in the "Traffic shaper changes…" tread ermal said (at every top of post):

if you enable the traffic shaper EVERY traffic that leaves any interfaces where the shaper is active will be shaped or better needs to be classified to a queue

Am I right that a simplest shaper config is the WAN-attached queies set only?

My setup with a two LANs and one WAN targeted mostly on intranet (LAN-with-OPT1) connectivity and only very limited external (WAN) access and by common sense I need no LAN-attached queies.
Am I right?