A lot of universities have started giving out unconditionals to people who have not yet completed their A levels as a way of tying them to the university so that they can be sure they are going to have people they want coming to them in September, instead of having to use Clearing to fill their courses. Many of these offers are only unconditional if the university is put as a firm choice. Otherwise it is a conditional offer.
This has many advantages for the university, but fewer for the applicant than they think. It tends to influence people into choosing a university they may not have chosen as their firm originally, because they are flattered or because they want the security of knowing they are in somewhere. That sometimes leads to complacency and not doing well in the exams because there is less incentive. It's important to realise that accepting an unconditional offer leaves you without an insurance - you can't fail to meet conditions if there aren't any - and without entitlement to enter Adjustment. You are effectively going to your firm whatever, unless you ask to be released into clearing and start from scratch there. Given the hundreds of threads started by members who suddenly discovered they wanted to go to their insurance and not their firm in the few weeks before results day, accepting an unconditional is a risky business.
Remember, it's for the university's benefit, not the applicants. It's done as a marketing strategy by universities and courses which may otherwise struggle to fill places. That's not a universal truth, of course, but it is for the majority of occasions. If you get an unconditional offer, put your cynical hat on and ask what's in it for them, as opposed to what's in it for you. If those two sides marry up, then that's great, but if they don't, don't be flattered into taking something you don't really want. It's not a sign that you are super-special.