Register online in case you need/want direct support from MSI in future. With MSI there's no time limit to do so other than warranty length I believe, i.e. you can register only if you actually need the support.
Also, under UK law (presently the Consumer Rights Act 2015) you can choose to return through the retailer. First 30 days through retailer you can choose full refund, instead of repair/replacement. 30 days to 6 months through retailer they have the right to one attempt at repair/replacement within 28 working days, otherwise full refund. 6 months to 6 years, if the damage isn't considered to be the customer's fault, they have one attempt at repair/replacement within 28 working days, otherwise a deprecated refund or other agreed solution with customer. The "6 years" should be considered as the lawful time limit to make a claim (you cannot make a claim beyond 6 years), not necessarily the duration of time a product should be supported. i.e If a manufacturer states 3 years warranty, take that as a guideline. Chances of success in making a claim after those 3 years would be very slim, and rightfully so - manufacturers can make cheap products and retailers sell these because there's a market/need/demand for them. It wouldn't be fair to demand 6 years warranty on every product, when corners have been cut to allow lower price-points, like PSUs with 2 years etc.
