There may come a time that you might need to transport you hamster and it’s important to be prepared just in case. It is quite likely that at some point during your hamsters life you will need to take your little guy to the vets so there’s no harm in having a travel cage just in case. Unless you wish to drag the entire IKEA Detolf to the vets! In all seriousness, it may also be handy to have a travel cage that you could use as a place for your hamster whilst your cleaning out the main cage, but even better it would be best to have a playpen for your hammy to run around in whilst you clean out their main cage.
Some people buy a smaller cage (By mistake) from the pet shop on the day they purchase their hamster and indeed a lot of pet shops sell that these smaller cages as just being starter caged and that you should upgrade. (This is an unacceptable excuse from the shops as it isn’t realistic to expect people to realise they need to buy a whole new cage again, and they are selling cages which are below the recommended size). Those who have upgraded to a bigger cage may choose to use the smaller cage they once bought as a transporter.
Plenty of Bedding so your hamster can burrow and some items of food should ensure your hamster is less stressed about the change in surroundings. Also it will probably be best for your hamster to be kept in the dark and not see top much of the big wide world, it could be overwhelming and a worrying experience.