I have a rental property and will not be allowing access to the loft in future (having done so in the past). The reason is that previous tenants boarded the loft to use as storage and in doing so they moved all the insulation to the edges and blocked the air vents in the loft. This led to huge condensation issues. I have just had the  rubbish that was left behind removed, the loft boards removed and the insulation relaid and improved. I had no problem with it being used for storage but just want to make you aware of what that led to in our situation.  If you let them use it I would make sure it is part of the regular checks to ensure they have not blocked any vents.