I agree its is a strange question to ask and so makes one wonder! But I would tend to think that they mean to be considerate rather than the opposite. Chancers and CFs usually stay quiet.
Silverflake I also think that your agent should be reassuring you what is in the contract regarding subletting.
I also think that you don't have the legal right to restrict or make specific conditions re guests (so long as they are temporary) as this impinges upon the right to quiet enjoyment etc. Morally I think it is absolutely wrong as well. Homeowners are simply not restricted in the same way.
But you are already protected.
Any noise or nuisance, or unreasonable damage caused by guests, parties, additional cars even, etc will (or should) already be covered in the tenancy agreement by nuisance clauses, and clauses against damage and subletting etc.
So when you already have these clauses, IMO putting additional specifications and limitations on guest stays is likely to be deemed an unfair and/or onerous term that conflicts with the tenants legal rights, and so even if you put them in the contract a judge might well rule them unfair and unenforceable. (search unfair terms in contract agreements, tenancy etc)
I know many LLs and agents want to put the frighteners on tenants so that they 'behave' (which is intimidation and coercion - homes are not optional so people sign because they have to live somewhere, not because they necessarily agree with the terms) but you have to think of this in terms of what can actually be enforced, and what sanction could be imposed. Short of criminal behaviour which is not the issue of the LL, sanctions can really only be (justifiable not punitive) monetary recompense or eviction.
If you actually tried to evict a tenant for breach of contract because they had an guest overnight without permission for example, a judge should dismiss it immediately as the punishment far outweighs the breach, and should rule it too draconian. Clearly the LL incurred no costs (except a ridiculous court case) so no money can be awarded, and so the clause is utterly pointless but has caused the tenant a lot of unnecessary stress. And the LL is frustrated simply because they misunderstood how the law works.
Too many LLs and agents rely on being able to intimidate and restrict perfectly nice tenants (not saying that's you OP, whilst the bad tenants will break any and every clause no matter what you write.
I am not a lawyer but have some relevant experience and you can read plenty of legal stuff that would support my views.
Also I think it is sensible to drop a card at the neighbouring properties giving the contact details of the managing agent and/or LL so that if the neighbours pick up on anything untoward they have someone to make aware. They might or might not be reasonable if they do complain, but I think it gives the LL some peace of mind that problems might be flagged up between inspections. And anyway it makes sense if there is any building works, issues with utilities etc.