Last year we got soffit vents installed and baffles and then re-insulated the attic. We are in a cold climate and only had about R15-R20 in the attic. We got the existing insulation removed so that we could check the wiring after a substantial mouse infestation in the attic. The electrical in this house has been dicey and when we got the feedback about the lack of insulation, the mice and put it together with what we knew about the wiring in the rest of the house, we decided to clear out the existing insulation. We had significant problems with icicles on the roof (enough that kids weren't permitted near the back of the house) Eaves troughs (gutters) were also not working well and had sagged so we had issues with water in the basement.
We consulted a couple of builders and two architects as well as the insulation companies.
No one felt that the roof vents and gable vents were sufficient.
In hindsight it would have been easier to have the insulation blown in while the soffits were off and had the baffles installed at the same time. Our roof is very low sloped so two of the insulation companies wouldn't even bid the job.
No icicles at all this past winter. I think the weight of the icicles was really hard on the gutters so this was good to get resolved. We didn't just cut holes in the plywood soffit - they were completely removed, including on the gable ends.
We did discover that the mice had not chewed any wires and that there was none of the weekend warrior wiring that was in the rest of the house. It was a fairly expensive bill for piece of mind. But now we don't have to worry about wiring, mold, a child getting impaled by an 8 foot icicle and our house is definitely warmer in the winter and cooler in the summer.