I broadly agree with David on this. Pensions and IHT might be another sub-category. UK taxation of foreign pension lump sums, has also become much more complicated since the 2017 reforms – so complicated that a firm of very competent CTAs recently asked me for an opinion for one of their clients .
In terms of the pension freedoms, where the pension pots are substantial, there may be a legal obligation on the client to obtain advice from an FCA regulated adviser (although when this applies is itself frequently misunderstood by pension providers). In such cases, I imagine some clients will not be keen on incurring a second level of cost by instructing a tax adviser as well. We obviously generally need to be careful also not to venture accidentally into the world of regulated financial advice.