Depends if going VFR or IFR, and whether the VMC-on-top option is available.
It's really easy to get a list of TAFs, and METARs before going, for every flight, along the route, so why not? You get an idea of the cloudbase, and also the forecast should indicate bad weather like TS or TSRA, CB, etc. Every pilot should do this, for a selection of airfields along the route. I do this even for flights at airway MEAs e.g. FL150. Of course one has to look at other sources for enroute weather but that wasn't what you asked about.
This will also give you an idea of the cloudbase en route.
It's rare to fly a route of any length with it being OVC002 all the way along underneath. Obviously one could not do this VFR with a UK PPL - well some people will always try flying under OVC002
It's an IFR or VMC-on-top issue really.
I think that overflying a 30nm area on which fog or very low cloud is forecast is OK. It amounts to an exposure lasting only minutes.
Overflying the Alps if covered in solid cloud is something else. There you have a 1hr or so exposure, with your only escape route being high enough, and having a GPS running a decent topo map so you can glide into a valley. The valley is
unlikely to have cloud all the way to the bottom. I don't think I would do a flight like that again though
It should be SCT or better, and a satellite pic is a good way to check that.
Approach planning minima is what is says on the plate!