Some people may be of the opinion that shoes-off in homes is a good idea in the damp of winter, but is quite unnecessary in summer, except when it rains (which it certainly does here in the UK).
However, on the contrary I maintain that shoes ought to be removed even in summer.
It is true that the weather is drier in summer,so there is less chance of bringing damp or mud into the house. However, in summer, shoes will still pick up small particles of grit. These particles gradually wear out carpets.
If you have laminate or wood floors, there is still the risk of making scratches (watch out with those high-heeled sandals, ladies) or leaving marks (why do you think you are expected to wear deck shoes or go barefoot on a yacht?).
Dust is still a problem in summer. Dust is not good for your health or your children's health and the less of it in your house, the better. There is likely to be even more dust in summer, as the ground dries up and cracks.
Dog dirt is still a problem in summer. In winter, many people will walk their dogs to the minimum that is necessary. In summer, people will be spending longer outisde with their dogs, increasing the risk of fouling up. Dog dirt is extremely unhealthy stuff. Not good for crawling babies. You may try to avoid stepping in it, but your shoes will still pick up small traces and then grind them into the carpet if you do not take them off.
There is also pollen, which is only a problem in summer. Your shoes will pick up lots of the stuff. If you suffer from Hayfever or you live with Hayfever sufferers, I recommend having a shoes-off policy in summer.
Of course, on a hot summer's day, nobody ought to mind taking their shoes off!